Teenage Pregnancy - What You Need To Know
It is clear that being a child of a teenage Mother often entails numerous risks: low birth weight, complications of the mother's pregnancy and delivery, and health problems associated with poor perinatal outcomes; greater risk of perinatal death; lower IQ and academic achievement later on, including a greater risk of repeating a grade; greater risk of socio-emotional problems; a greater risk of having a fatal accident before age one; and finally, a greater probability of starting one's own family at an early age. Although there are variations from study to study, most studies that survey a representative sample from a population that has had no special interventions and is of diverse socioeconomic makeup, and that do not control for SES or other factors, find that children of teen parents are at greater risk than children of older parents for a host of health, social and economic problems.
The critical objective, of course, is to explain why being a child of a teenager entails these risks. This is important because it affects the way we plan interventions to prevent undesired outcomes. The implications of an outcome due to physical immaturity (or, in the case of an older mother, the aging process) are different from those that are due to inadequate prenatal care or to inadequate nutrition, to poverty or to ignorance. Explanation is, therefore, the goal of this chapter, which is divided into several sections, each focusing on a specific outcome: health; cognitive development and school achievement; and socioemotional development. The fourth section focuses on intervening factors: e.g., family structure, socioeconomic status, and maternal education. It also looks at the part parenting behaviors play in distinguishing adolescent from older parents and the influence of such behaviors in mediating child outcomes. Finally, the last section focuses on methodological issues and substantive issues that need further research.
Two major data sets are used in this chapter, the Collaborative Perinatal Project (CPP) and the Health Examination Survey (HES). The CPP included all patients or a random sample of all patients qualifying for prenatal care in the 12 participating medical centers during 6 years of intake (1966–1973). The total sample size was 53,625. The children of respondents were followed at ages 6 to 8 and a subsample was again followed-up at about 12 years of age.
Cycle II of the Health Examination Survey (HES), conducted in 1963– 65, consists of a national random sample of 7110 children age 6–11. The children were given health and psychological exams. Information was also collected from the mother, the school, and from the birth certificate.
Cycle III of the HES, conducted in 1966–70, consists of a national random sample of 6768 youth 12–17. The information collected is the same as in Cycle II, with the addition of a questionnaire filled out by the Youth. A small subset of children interviewed in Cycle III had also been interviewed in Cycle II.
HEALTH
Perinatal Mortality1
The first outcome of interest is perinatal mortality. A number of studies (see Strobino, this volume; also Makinson, 1985) report a higher incidence of perinatal mortality among teenage mothers. These studies show the relationship between mother's age and perinatal mortality as a J-shaped function. That is, it is high at very young ages, declining to a low point in the mid-twenties, and then climbing again among older mothers. The evidence is consistent that perinatal problems increase among mothers above age 30; however, recent evidence from the Danish Perinatal Study and from the Collaborative Perinatal Project in the U.S. show a linear relationship between maternal age and perinatal mortality with low rates among young women, and increasing rates with maternal age (Mednick and Baker, 1980)—or that there is no relationship (Broman, 1981), at least for ages 12–29.
There are two major types of explanations for the often found association between young age of mother and higher incidence of perinatal problems. First, it is hypothesized that the teenager is physiologically immature; thus her less desirable outcomes (see for example, NCHS, 1984:10). A second explanation is the differential social characteristics of teenage mothers-lower SES, lack of access to prenatal care, poor nutrition, poverty and ignorance (see, for example, Baizerman, 1977; Mednick and Baker, 1980). Whatever explanations are used (and different ones may hold for different age groups) should account for the higher levels of perinatal problems among both teen and older mothers.
In both the Danish and the U.S. Perinatal studies, relatively high risk groups were overrepresented.2 However, Mednick and Baker (1980: 38) argue convincingly that “In view of the unusually advantageous treatment conditions prevailing in the university hospital samples as a group, the teenage mothers in these samples probably received considerably more intensive and higher quality treatment than teenagers in the population at large.” Because a clear relationship does exist between quality of medical care and perinatal mortality rates (Mednick and Baker, 1980:39–40), the latter argue that
The relatively lower mortality rates observed among the teenage subjects, compared with the rates in older age groups in the American and Danish Perinatal samples, are due to the provision of adequate pre- and perinatal medical treatment…the previously reported higher mortality rate associated with teenage deliveries was not caused by physiological characteristics of the teenage organism but rather by social factors that have the ultimate effect of lowering the quality of medical treatment received by teenage mothers in the general population.
In contrast, constitutional changes do appear to determine the increased risk of perinatal mortality with increasing age of mother at birth. The results from studies of representative samples as well as from special hospital samples show a similar relationship for mothers over 30; increased age appears to be associated with increased rate of death (Mednick and Baker, 1980).
Neonatal Health
Vital statistics data (NCHS, 1984) show that children of teen mothers are more likely to be below 2500 grams at birth than children of mothers 20 to 39, and the younger the age of the mother the higher the proportion of infants of low birth weight. In 1982, twice as many infants of 10–14 year olds (13.8 percent) were low birth weight as infants of 20–24 year olds (6.9 percent). In that year 9.3 percent of the infants of 15–19 year olds were low birth weight. Low birth weight babies are subject to higher risks of death, mental retardation, and other health problems (Williams and Chen, 1982). Low birth weight has also been implicated in poor intelligence and achievement test scores in childhood (see, for example, Edwards and Grossman, 1979; Mednick and Baker, 1980).
A second measure of neonatal health is the Apgar score. The Apgar score is a summary measure used to evaluate the neonate's overall physical condition at birth. It is a composite evaluation of five factors—heart rate, respiratory effort, muscle tone, irritability, and color—each of which is assigned a value from 0 to 2. The overall score is the sum of the five values, with a score of 10 being optimal (NCHS, 1984:12). Infants of teen childbearers are more likely to score under 7 at either one or five minutes after birth than are infants of mothers 20 to 39. These results hold for both blacks and whites, though the proportion of low birth weight infants and the percent with low Apgar scores are consistently higher among blacks than among whites.
Although these relationships appear to hold in the population as a whole, there appears to be little difference between children of adolescent and non-adolescent mothers in special samples where prenatal and postnatal care are good. Sandler et al. (1981) evaluated the relationship between the age of mother and two measures of newborn behavior: 1) the Neonatal Behavioral Assessment Scale (Brazelton) and 2) a measure of infant temperament (Carey “My Baby” scale). No differences were found on the Brazelton Scale or Carey scale between children of adolescents and post adolescents (age not defined) within the first few days after birth.
Lester et al. (1982, 1983) used the Brazelton Scale on the second day after birth of a sample of Puerto Rican and American infants of teen mothers. In addition they obtained information on a number of health measures from medical records. In a regression analysis controlling for ponderal index, gestational age, marital status, drug score, 1 minute Apgar and the number of maternal parturitional and fetal nonoptimal conditions, none of the associations between maternal age and Brazelton scale cluster scores were significant. There did appear to be an interaction in the Puerto Rican sample between a complications index and age. Infants of young mothers with few complications had a wider range of states of arousal than infants of older mothers with few complications.
In both these studies (Sandler et al. and Lester et al.), mothers received excellent prenatal and postnatal medical care through a special program for low income families. A number of recent studies failed to find any difference by age of mother in health status of neonates at birth (Apgar score, birth weight, prematurity, birth trauma, etc.) once initial differences such as differences in SES between adolescents and non-adolescents were controlled (Zuckerman et al. 1983; Rothenberg et al., 1981). Net of SES, Broman (1981) found older women to have higher birthweights among blacks, but not whites. Also net of SES, Broman (1981) found the youngest adolescents (12–15) to have lower Apgar scores than older adolescents among whites and blacks. The differences were very small, however.
Infant Health Status
The medical risk to neonates of adolescent childbearers does not appear to be biological, but, rather, due to differential access to adequate medical care (Mednick and Baker, 1980). Less research has focused on the effect of age of mother on the health status of infants, that is from the first 28 days to one year of age.
Two studies have addressed maternal age differences and infant health status (Hardy, 1978; and Mednick and Baker, 1980). Hardy presents one figure which shows that the risk of infant death after the neonatal period is higher for the infants of black teen mothers than for the infants of black older mothers. However, no differences among whites by age of mother at birth were found. This study did not control for the SES of the mothers, however.
The Mednick and Baker (1980) study, using Danish data, looked at the physical health status of the infant at one year as an outcome measure (see Makinson, 1985, for results of other non-U.S. studies). They found that the relationship between mother's age and infant's first year physical health status was curvilinear. That is, infants of mothers under 20 and over 35 were the healthiest; those of mothers in their twenties had the most health problems. Comparing neonatal and one year outcomes, children of the youngest mothers were the best off at both points. In contrast children of older mothers were less well off at birth, but very well off at one year. This suggests different mechanisms influencing the different outcomes at two points in time: biological factors at birth, environmental factors at one year. Older mothers may have the most biological problems but the best environment. Age-related social variables may be enough to compensate for the negative biological effects seen at birth. Mednick and Baker show that the most important predictors of health status at one year were birthweight and being female. After controlling for these important factors, a number of environmental factors were associated with better child health, including an older mother, fewer previous pregnancies, and less exposure to institutional day care.
Why the infants of Danish mothers under 20 were healthiest at one year also needs explanation. Mednick and Baker hypothesized that teen mothers may have older adults to rely on for support. They found that infants living with their grandmothers had the best mean health score; infants living with both biological parents a mid-range score, while infants who lived with their unmarried mother or in an institution or foster home showed the worst scores at one year. In one analysis, after controlling for birthweight and pregnancy complications, number of nurturing adults was strongly related to a positive one year health status among children of teen mothers. Mothers in their twenties may lack the parental support of the young mothers as well as the maturity and experience that come with age.
In conclusion, it appears that once the birth occurs and survival is assured, health status varies strongly with social and environmental variables. In the case of the older mother, age implies a number of positive psycho-social and environmental aspects. In the case of the young mother, it may imply the availability of alternative caregivers to help out. The worst one-year outcomes occurred among children of 18–29 year olds. “Once infant survival is assured, environmental and social variables begin to emerge as important to the continued physical growth and development of the child” (Mednick and Baker, 1980:65).
Path Analysis of Infant Health Status at One Year
The previous analysis of health status at one year did not control for a number of other factors that might affect health: health status at birth or complications of pregnancy and delivery. The question is whether there are residual effects of non-medical variables that may impact on one year infant status. A number of studies (e.g., Sameroff, 1979) have shown that environmental factors do not have major effects on cognitive and neurological measures within the first 12 months of life. Measures of infant physical health and motor development have been shown to be sensitive to variations in prenatal environment. Good perinatal care can insure good perinatal outcomes even when environmental conditions are less than adequate. During the first year of life, environmental influences may increase in importance as the positive effects of good prenatal care wear off. Intervention postnatally is less common than prenatal medical intervention. During the year after birth, the Danish cohort studied by Mednick was more similar in medical care to the general population. Thus effects of environmental factors could be expected to show at one year.
Mednick and Baker (1980) developed a path model to trace the causal connections between background, mother's age, and intervening medical and health factors on one year infant outcomes. Background factors (spacing, mother's age, previous health, data on previous pregnancy, wantedness, use of institutional day care, SES, mother's employment and family size) were assumed to predict one year infant outcome through the following health and medical variables: complications of pregnancy and delivery, multiple births, birth weight, and neonatal physical and neurological status. Two random samples were pulled from the full sample and models were tested separately on each sample. Unfortunately the results differed substantially between the two samples. Mother's age did not have a consistent direct or indirect effect on one year physical or neurological status or one year motor development. In sample 1, older mothers had children with poorer one year physical status. In sample 2, older mothers had children with better one year neurological status (direct effect) and better one year motor development through improved neonatal physical status (indirect effect).
However, given that the same findings don't hold up in both samples, there appears to be no consistent direct or indirect effect of mother's age on infant status at age one. Infant status at age one was influenced directly by birthweight and neonatal neurological status and indirectly by neonatal physical status. In addition, exposure to institutional day care significantly reduced rating of health status at one year. Thus mother's employment showed an indirect effect via daycare on one year health status. Higher birthweight was associated with improved one year motor development.
The analysis supports the conclusion that neonatal status is strongly influenced by factors subject to medical intervention. Maternal age, SES, and even previous pregnancy history effects on neo-natal health are weak in a sample which received excellent medical care. By age one, neonatal status exerts the strongest influence on physical and motor status. Although none of the expected background factors has an impact at age one, environmental influence on physical status can be seen through the direct (negative) impact of institutional day care, and the indirect (and also negative) influence of maternal employment.
This analysis assumed a linear relationship between maternal age and outcomes. In fact, other analyses by the same researchers have shown a non-linear relationship. The weakness of maternal age effects may be due to differential influences across the life cycle. Finally, this analysis did not and could not include the potential ameliorating influence of other adults in the home for the very young mother.
Thus although high quality medical care appears to have reduced the environmental influence on children's health over the first year, there is evidence that social conditions, which did not have an impact during that first year, at one year do have an impact.
Fatal Infant Accidents
Further evidence for the importance of environmental factors is found in a study using linked birth and death records from North Carolina and Washington State for 1968 through 1980. Wicklund et al. (1984) found a strong inverse relationship between maternal age and mortality rates from accidents for children under one, net of parity and educational level of mother (a proxy for SES). The actual mortality rate from accidents during the first year of life is actually quite low—in 1980 in North Carolina about 3 out of 10,000 live births died from accidents in the first year in Washington state the rate was 1.47 per 10,000 live births. There were substantial differences by race, maternal education and age of mother, however. Children of mothers under 20 who had 9 or more years of schooling were substantially more likely to die from accidents in the first year of life than children of mothers 20 and over with the same amount of schooling. Among children of mothers with very low levels of schooling, those with mothers 24 and younger were more likely to die than those with mothers 25 and older. Education was also strongly inversely related to infant mortality from accidents and parity was directly related. That is, mortality rates were lower for children with a more educated mother and one with fewer children. Black children had almost twice the rate of deaths from accidents in the first year as white children.
The leading causes of infant accident mortality in North Carolina were suffocation by inhalation and/or ingestion of food, and suffocation by mechanical means (e.g., in bed or cradle, by plastic bag, etc.), with transport accidents coming third. In Washington State, transport accidents were the leading cause, with mechanical suffocation and food suffocation next. Parental care is crucial for the safety and well-being of children; and such parental care appears to be less dependable among families in which the mother is young, black, less well-educated and has more children.
Neuropsychological Status/Motor Development
The Collaborative Perinatal Project was originally designed by the National Institute of Neurological and Communicative Diseases and Stroke (NINCDS) as a study of the neurological problems of children. Children were assessed at age four using the Graham-Ernhart Block-Sort, a battery of fine-motor development tests and a battery of gross-motor development tests. The Bender-Gestalt test was the main measure of functioning for seven year olds. These tests measure motor functioning and development, an indicator of brain damage.
Three studies using the CPP have looked at the association between age at birth of the child and motor development. Marecek (1979) found no consistent evidence for a relationship between age at first birth of the mother and the child's motor development at age 4. At age 7, Marecek found a slight curvilinear relationship such that children of both older and younger mothers do slightly less well on the Bender-Gestalt test than children of mothers in their late teens and early twenties. Hardy et al. (1978), in contrast, using the Baltimore subsample of the CPP, found a significant difference in scores on the Bender-Gestalt test at age 7, favoring the children of older mothers.
Neither of these studies controlled, however, for differences in socioeconomic status of the family. Controlling for SES, Broman (1981) found that both gross and fine motor scores of 4 year olds were lower among children of black adolescent mothers than black older mothers. Only the gross motor scores were lower among the children of white adolescent mothers compared with the children of white older mothers. No analysis of motor development was reported by Broman for children age 7.
Because the results appear to be inconsistent it is reasonable to conclude, as did Marecek, that there is no evidence of a real or substantial difference in motor development/brain damage by age of mother at first birth (Marecek) or age of mother at birth of index child (Broman and Hardy et al.).
COGNITIVE DEVELOPMENT AND SCHOOL ACHIEVEMENT
The major source of data on infants and young children is the Collaborative Perinatal Project (CPP). Although a number of different researchers have utilized data from this study in their analyses, the subsamples they have used have been slightly different. As a result, the results should not be expected to be identical. Marecek (1981) used the Philadelphia subsample of the survey in her study, Hardy (1980) used the Baltimore subsample, while Belmont et al. (1981) and Cohen et al. (1980) and Broman (1981) used the entire sample of respondents and their children. Although blacks were overrepresented in the entire sample, they were especially predominant in both the Baltimore and the Philadelphia samples. These sample hospitals served a primarily black, low SES area of their respective cities. Thus the results from Marecek and Hardy may differ from those of the other studies.
Infants
The Collaborative Perinatal Project assessed the developmental status of infants at 8 months using the Bayley Scales of Infant Development and the Infant Behavior Profile. The Bayley Test consists of two separate scales: the Mental Scale and the Motor Scale. The Infant Behavior Profile was designed to evaluate qualitative aspects of children's behavior. Finally, the 8 month exam includes summary ratings of general development based on evaluations of the examiners
Marecek found that, among blacks, first born children of mothers under 20, as a group, scored lower on the average than first born children of older mothers on the Bayley mental scale. Among whites, in contrast, first born children of mothers 20 to 25 scored lower on the average than children of mothers 18 to 19; children of mothers under 18 did not differ from the other groups. Differences are very small, however. The author then looked at the individual components of the scale. Black children of women under 20 scored lower on three components than black children of older mothers—incidental spontaneous exploration, social interaction, and awareness of object constancy. In the white sample, children of mothers under 18 scored lower on 2 components—incidental spontaneous exploration and ability to sustain attention than children of older mothers. On the Bayley motor scale there were no differences by mother's age at first birth for blacks or whites.
Ratings on the Infant Behavior Profile ranged from 1 to 5, with an extreme underresponse to physical stimuli rated 1 and an overresponse rated 5. Among whites there were no differences by age of mother. Among blacks, age of mother at first birth had an effect on three ratings. Black children of childbearers under 20 were likely to be rated weak in their responses to physical stimuli, with black sons of adolescent childbearers more likely than black sons of older childbearers to be slow in their responses. Children of older childbearers were more likely to be overly apprehensive in response to the examiner relative to children of younger childbearers. However, only a very small proportion of the sample was in either of the extreme categories—1 or 5.
On the summary ratings of black children's development (as rated by a pediatrician on a three-point scale—normal, suspect or abnormal) age was not related to development for daughters. For sons, age was related to development. Twice as many sons of childbearers under 18 at first birth were rated suspect compared with sons of mothers 18 and older at first birth (9.2 compared with 4.1 percent). There was no relationship for whites.
Marecek draws two conclusions: 1) The effects of maternal age on infant mental development are small, and 2) Maternal age is more likely to affect boys' development than girls'. Thus on these measures little difference was found between children of older and younger mothers.
Marecek did not control for SES. In her study using the entire CPP, Broman examined the relationship between age and Bayley scale score within SES categories. Broman also found differences by age net of SES, with Bayley mental and motor scale scores higher among infants of younger (13–15 and 16–17) than older mothers (20–29). Since the differences in both studies are small, and they operate in different directions, the conclusion would appear to be that there is little difference on these measures between children of older and younger mothers.
Early Childhood
The Collaborative Perinatal Project (CPP) used the Stanford-Binet Intelligence Scale to measure the intelligence of children at age 4. Using this measure, Hardy et al. (1978) found a significant difference in IQ score at age 4 between children of black mothers who bore that child at 17 or younger and those who were 20 to 24 at that birth. The difference is about 4 IQ points on the average. There was no difference for whites.
Marecek also failed to find a difference on the Stanford-Binet by age at first birth among whites. Among blacks, age of mother at first birth had no significant effect on girls' IQ but had a marginally significant effect for boys (probability less than .08). The sons of mothers under 18 scored lower on the average than those of mothers 20 to 25 at first birth, with those of mothers 18 to 19 intermediate. Marecek finds that among children of childbearers under 18 and 18–19, boys scored lower on the average than girls, while there was no sex difference among children of mothers 20 to 25 at first birth. As a result, she concludes that boys tend to be affected more strongly by mother's first birth age than girls. Controlling for SES, Broman (1981) found a 5–6 point difference in IQ at age 4 between both black and white children of older and younger mothers, favoring the former. SES effects were larger than age effects, however.
Furstenberg (1976) also found a difference in cognitive performance between black children of adolescent parents and black children of classmates who delayed childbearing until age 18, even when differential school attendance was controlled. Cognitive performance (as measured by the Preschool Inventory) was higher among comparison group children.
Middle Childhood
Intelligence
The CPP measure of intelligence used for children age 7 was the Wechsler Intelligence Scale for Children (WISC). The WISC consists of two major scales: the verbal and the performance scales, each with 6 subtests. A subset of 7 subtests of the WISC was used on the Collaborative Perinatal Study, three verbal (information, comprehension, vocabulary) and four performance (digit span, picture arrangement, block design, and coding) subtests (Marecek, 1979).
In the Marecek study, no difference in intelligence by mother's age at first birth was found for whites. Among blacks, both Hardy and Marecek found differences by mother's age at first birth. As a group, children of childbearers under 18 tended to do less well than children of later childbearers. However, Marecek found a sex difference here. The relationship was curvilinear for daughters, linear for sons. As a group, daughters of mothers 18–19 tended to do best; sons of mothers 20–25 tended to do best. In addition, sons of childbearers under 18 tended to do less well than daughters of childbearers under 18. However, there was no sex difference among children of later childbearers. This again suggests a stronger impact of maternal age on boys on the average than on girls.
There were several differences among blacks by type of scale. On the performance scale, sons of 20–25 year old mothers scored highest; daughters of 18–19 year old mothers scored highest. On the verbal scale, sons of childbearers 20–25 scored highest. On the same scale daughters of childbearers 18–19 scored higher than daughters of childbearers under 18 with little difference between daughters of 20–25 year olds and 18–19 year olds.
Marecek (1979) estimated path models of the direct and indirect effects of adolescent childbearing on WISC scores. These models were developed only for blacks, since the white samples were too small for meaningful analyses. The variables included were age of mother at first birth, mother's education, mother's marital status, number of parents in the household, per capita income, and child's behavior control. The results showed no direct effect of mother's age at first birth on child's IQ score. There were small indirect effects through mother's marital status, number of parents in the household and per capita household income which were stronger for males than for females. The models were, unfortunately, unable to explain much of the covariance in terms of other variables in the model, either because 1) some important intervening factors may have been left out or 2) there may be some direct effects not captured by the variables in the model. The total correlation between age of mother at first birth (1-under 18; 0=18–25) and IQ score was −.042 for males on the verbal scale, −.102 for males on the performance scale, −.105 for females on the verbal scale and −.017 for females on the performance scale. The total indirect effects identified were −.038, −.039, −.024 and −.014 respectively.
The results suggest that age of mother is related to both verbal and performance IQs among black male children but only to verbal IQ among black female children. However, the relationship is very small, accounting for less than one percent of the variance in children's IQ scores, and, furthermore, is indirect (Marecek, 1979). Of course, the sample was relatively homogeneous with regard to SES, and mother's age was restricted to a maximum of 25 years.
Broman (1981) found, using the whole CPP, that scores on the WISC for seven year olds were only marginally associated with maternal age among whites, and unrelated to maternal age among blacks, controlling for the effects of SES. SES effects were very large, in contrast.
The second major national study which collected data on children is the Health Examination Survey (HES), Cycles II and II. Cycle II collected data on children 6 to 11 in 1963–65 and Cycle III collected data on children 12–17 in 1966–70. There is some overlap in the samples of Cycles II and III, that is, some of the same children were interviewed in cycles II and III. Belmont et al. and Cohen et al. both used Cycles II and III as well as the Collaborative Perinatal Study. Levin (1983) used cycles II and III of the HES only. Davis and Grossbard-Schectman (1980) used Cycle II of the HES. Two subtests of the WISC, vocabulary and block design, were included on the HES.
Belmont et al. attempted to address the issue of whether there was a unique disadvantage for children's intelligence of having a mother who was a teenager. Thus they used a measure both of mother's age (in years) and a dummy variable indicating whether or not the mother was a teenager at the birth of the study child. They found a linear relationship between maternal age and the IQ score of the child (WISC) in all three surveys; however, they found no evidence of excess disadvantage to the offspring of mothers under 20 above and beyond the linear relationship. (For example, children of mothers age 20 do less well than children of even older mothers).
Belmont el al. found the contribution of maternal age in years to be very small, contributing less than 1 percent of the variance explained in intelligence. The contribution of teenage mother status was even smaller. The most important factor explaining variance in child's intelligence was education of the parents. Family size, age and sex of the child were also important. They found some interesting subgroup differences and interactions. In particular, they found that the impact of mother's age at birth of the study child was stronger among 6 year old than among 11 year old children. It was stronger among urban than rural children, among blacks than whites, and among children in larger families. IQ scores were lower for blacks than whites overall. Finally, scores of children in the CPP, which is from a lower SES population, were lower than those of children in the HES Cycles II and III.
In general, the results from the three data sets were very similar. The authors' (Belmont et al.) conclusion was that the offspring of teen mothers suffer IQ depression only because of associated social disadvantages and not because of any “immaturity of the mother.”
Cohen et al. (1980) also conducted a path analysis on these data to attempt to tease out some of the causal sequences leading to lower intelligence scores of the children of teen mothers. Here again, the authors looked at the influence of maternal age in years as well as whether the child's mother was under 20 or 20 and over. There was no direct effect of teen maternity on the child's IQ. The results showed that the effect of linear maternal age was significant in five of the six samples (three surveys and two race groups) after controlling for a number of other factors. The exception was blacks in Cycle III of the HES. The size of the effect was rather small, however; approximately .09 to .21 IQ points per year of maternal age. Again, the results from the three surveys were similar. There was no apparent difference either by age of child (6–11 versus 12–17) or by type of population (low income versus all income levels).
The effect of maternal education is much larger—approximately one IQ point per year of maternal age among whites, somewhat less (.4 to .9) in the black sample (Cohen et al.). The effects of paternal education were smaller. Maternal employment had inconsistent effects—a negative impact in HES Cycle II and a positive impact in the CPP. Father absence and large family size both had negative effects on IQ.
Even though teen maternity (being a child of a teen mother under 20 compared with being a child of a mother 20 or older) had no direct effect on IQ, it had several indirect effects (Cohen et al.). The largest of these was through maternal and paternal education. The total mean IQ difference for whites ranged from −2.45 in the HES Cycle III to −2.71 in the CPP to .4.22 in HES Cycle II. Among blacks the indirect effect was only significant in the CPP, 1.00 IQ point. Teen mothers were more likely to have had less schooling, which reduces their children's IQ. Family structure had a smaller, but significant impact. Children of teen mothers were more likely to live in homes not headed by both biological parents, and this was associated with lower IQ scores. As a result the total mean difference between the IQ scores of white children of teen mothers compared with those of white children of older mothers ranged from .2.45 in the HES Cycle II to −2.71 in the CPP to −4.22 in HES Cycle II. The IQ scores of black children of teen mothers were significantly lower by one IQ point only in the CPP.
Linear maternal age had both direct and indirect effects. Here the direct effects dominated (Cohen et al.). The major indirect effects operated through family size, in particular the number of births subsequent to the study child (since birth order is also controlled). Delaying a first birth one year was associated with a rise in IQ of from .09 IQ points (HES, III) to .25 IQ points (HES,II) for whites.
Levin (1983) also used the HES survey, Cycles II and III. He found significant effects of mother's age at birth of the study child on WISC vocabulary and block design scores, as well as the two subtests together, controlling for sex and age of child. These relationships did not disappear when controls were introduced for race, birth order, income, education, household structure, household size and ecological factors. However, as the author pointed out, the sizes of the effects are small mother's age at birth explains less than half of one percent of the variance in cognitive variables controlling for other factors. Total variance explained ranges from .18 to .33.
Davis and Grossbard-Schechtman analyzed Cycle II of the HES. Their study focused on 10 to 11 year olds. They explored the impact of two different variables: mother's age at birth of index child and whether or not the mother was an adolescent (under 18) at birth of the study child. Children of mothers 40 and over were excluded from the study. The authors concluded that, net of other factors, having a mother who was an adolescent did reduce the scores on the WISC. However, the differences were only marginal. Having an adolescent mother was associated, on the average, with an IQ score lower by 2.14 points on the vocabulary scale (marginally significant at p .10) and by 2.15 points on the block design scale (not significant). Thus the effects of these variables were relatively small. Having a mother with a low level of education was more harmful—approximately one IQ point for each year of schooling.
According to Davis and Grossbard-Schechtman, the age of mother (in years) appeared to significantly affect WISC vocabulary scores, but not block design scores. The effect also appeared to be non-linear. At higher levels of age, the scores appeared to turn down slightly. The effect of maternal age on vocabulary scores was small—it increased about one half of one IQ point for each year of maternal age. This effect held net of a large number of other factors, including health factors. Maternal age had a significant but very small impact on grade retention. Again this effect was slightly non-linear. The probability of repeating a grade dropped as age of mother rose, but rose again slightly among children of older mothers. There was no association of age of mother with child's reading score. Finally, boys' vocabulary scores appeared to be affected more strongly than girls' by mother's age at birth. A boy's score increased with mother's age until the mother reached age 35; afterwards, the older the mother, the lower the boy's score on the average.
A third nationally representative survey of children has also been used to study the relationship between parental age at birth and the child's intelligence (Moore et al., 1985). This survey, the National Survey of Children, collected data in 1976 on 2,301 children aged 7–11 in 1,747 households. Interviews were conducted with the eligible child (or two eligible children if there were two or more children in the household), and with the parent most capable of providing information about the child, usually the mother. In addition, school information was obtained on 1,682 of the children. Not all the children are first born, although the analyses examine the impacts of the age of mother at first birth. The measure of intelligence used in this data set is the Peabody Picture Vocabulary Test, a test that measures both innate ability as well as stimulation in the home environment. The results show that children of teen mothers are less likely than children of older mothers to do well on this test, a result which is statistically significant for whites but not for blacks (Moore et al., 1985). When the data are adjusted for the effects of mother's education, family configuration, sex of child, family income, number of siblings, and number of moves in last five years, the differences between children of mothers younger and older at first birth decline sharply. Although children of youngest mothers generally have the lowest scores, among whites and blacks the children of the very youngest mothers at first birth (those less than or equal to 15), in fact, have high scores relative to children of older mothers. Additional analyses conducted by these researchers suggest that what differentiates the scores of children is whether the mother dropped out of school at an early age and didn't return or whether she continued in school/ returned and completed more schooling later on. The very earliest childbearers may be the most likely to continue/return to school and, as a result, their children may not suffer as much. However, this is still speculation, as no research yet shows this to be true. Furstenberg and Crawford (1980) suggest that those who remain at home are more likely than those who leave to obtain more schooling.
Achievement
The CPP and HES measured school achievement using the Wide Range Achievement Test, which includes subtests on spelling, reading and arithmetic. The purpose is to measure skills, not intelligence. A second measure of achievement is whether or not the child had repeated a grade of school by the time of the 7 year exam, and the mother's evaluation of the child's success in school, as reported at the 7th birthday.
Using data from a white middle and working class Northeastern community, Kinard and Reinherz (1984b) looked at children prior to entry into school, at the end of kindergarten, at grade 3, and again at grade 4. The test used at time one was the Preschool Screening System. In grade 4 the Short Form Test of Academic Aptitude and the California Achievement Test 70 were used. In addition, ratings of school performance by parents and teachers were obtained at the end of grade 3. Parents rated school achievement on a five point scale and completed the Child and Adolescent Adjustment Profile (CAAP) of Ellsworth. Teachers assessed child's reading, arithmetic and overall academic achievement on a five point scale and also completed the Ellsworth scale.
Kinard and Reinherz found that, controlling for sex and maternal education, maternal age had a main effect on only one measure: information processing skills at preschool. Children of late adolescent (18–19) mothers had lower scores than children of either early adolescent or older mothers. However, this effect did not persist over time: no difference was found at grade three or grade four. There was no effect of maternal age on achievement and aptitude test scores or on teacher and parent ratings of performance. Maternal education was the major factor affecting cognitive and achievement scores, with substantial and consistent differences on almost every measure favoring children of better educated mothers.
Vincenzi and Brewer (1982) used two samples of children, one in grade 4 and one in grade 6, from a primarily black low income area, to look at the school achievement of children of teen mothers. They found an impact of having a teen mother only for children with no preschool or kindergarten experience. Controlling for SES, AFDC receipt, and initial achievement level, children of teen mothers with no preschool or kindergarten experience tended to have lower reading scores, more absences and were more likely to be retained in grade than children of non-teen mothers with no preschool experience. In addition, the achievement scores of children of teen mothers were helped more by preschool and kindergarten than the scores of children of non-teen mothers.
The results reported by Marecek based on the CPP show among blacks a linear relationship of age of mother with scores on the three subtests of the WRAT. Children of adolescent childbearers scored lowest. On the reading subtest age of mother at first birth was a stronger predictor of scores for boys than girls. For whites, the age at first birth of the mother affected scores only on the arithmetic test, and there was no sex difference.
Broman (1981) found that children of young mothers (12–15) and 16–17 were more likely to have below average scores on the arithmetic, reading and spelling subtest of the WRAT. For example, as the mother's age increased from 12–15 to 20–29 the percent of white children scoring low decreased from 8 to 4 percent. Among blacks the percent of low scorers decreased from 19–5 to 15–5 percent. These results controlled for SES differences between younger and older childbearers.
Levin (1983) used the HES survey. Results are similar to those found with the WISC: significant effects of mother's age at first birth on the WRAT arithmetic and reading scores, as well as the full test, after controlling for sex and age of child. These relationships do not disappear when controls are introduced for race, birth order, income, education, household structure, household size and ecological factors. However, as the author points out, the sizes of the effects are small; mother's age at birth explains less than half of one percent of the variance in cognitive variables controlling for other factors. Total variance explained ranged from .18 to .33. Mother's age is also associated with ratings of child's exceptional performance, academic difficulty, and precociousness. However, when other variables are controlled, only the relationship of mother's age with exceptional performance is still significant. Again, the percent of variance explained is very small.
Marecek found that, among whites, mother's age at first birth is unrelated to grade repetition. Among blacks she found a higher repetition rate among children of childbearers under 20 at first birth. Controlling for race, Davis and Grossbard-Schechtman found that having a mother who is young at birth of the study child does increase grade retention (indirectly through IQ). In addition, the impact of mother's schooling was found to be more significant for adolescent than for older mothers in keeping the child at grade level. That is, having an adolescent mother with one additional year of schooling decreased grade retention by almost 50 percent. In contrast, having an older mother with one additional year of schooling reduced grade retention by only about 10 percent.
Moore et al. (1985) found a strong relationship among blacks and whites between age at first birth of the mother and being behind grade for age among 7 to 11 year olds: children of younger mothers were more likely to be behind grade. The difference was substantially weakened, although it did not disappear, when controls for other variables— mother's education, family configuration, sex of child, family income, number of siblings, and number of recent moves—were added to the analysis.
Among whites, Marecek found no relationship between age at first birth of mother and mother's reports of learning disturbances in their offspring. In the black sample there is a significant relationship with age at first birth among males. Nearly 12 percent of boys born to childbearers under 20 were rated as having a learning disturbance compared with 4 percent of the sons of older mothers.
Thus there appears to be an effect of mother's age at first birth on school achievement and grade repetition. This effect is stronger for blacks than for whites and for boys than for girls. However, the effect is very small and is not found in every study.
Adolescence
Several studies have looked at adolescents: Levin (1983), Card (1978); Belmont et al. (1980). The effects of maternal age do not appear to weaken as the children grow older. Levin (1983) finds similar relationships between age of mother at birth of child and IQ and achievement scores among 12 to 17 year olds as among 6 to 11 year olds. Net of sex and age of child, mother's age at birth is significantly associated with scores on the WISC and WRAT tests and subtests, with exceptional performance, and with ratings of academic difficulty. None of these relationships disappear when additional variables (race, birth order, income, education, household structure, household size and ecological factors) are controlled. As before, however, the proportion of variance explained by mother's age is very small—under 1 percent. Total variance explained ranges from 20 to 35 percent.
Card (1978) looked at teens at age 15 and 17. An adolescent mother was defined as a mother less than 20 (for those who were age 15 in 1960) or a mother less than 18 (for those age 17 in 1960).3 in both cohorts children of adolescent parents had lower scores than their classmates on cognitive tests; they also had lower educational expectations. The cognitive differences were about .4 standard deviation in magnitude. However, when other factors were controlled, these differences declined. A change of one standard deviation in the proportion of the sample who were adolescent parents was associated with only about a one point change in IQ score.
Card (1978) also developed a path model. Besides the small direct effect of having an adolescent parent on academic aptitude, there was a substantial indirect effect through family structure. Children of adolescent parents were much more likely to be living with only one parent than children of older parents, and children in one-parent families had significantly lower aptitude scores, grades and aspirations.
Card concluded that the cognitive consequences of adolescent parentage were more severe for male than female children since she found that although in the comparison group males had higher mean academic aptitude scores than females, among children of adolescent parents, females had higher scores.
Mednick and Baker used data from the Danish Longitudinal Study to examine youth age 17 to 19 in 1979. They, unfortunately, did not have test scores on youth. However, they obtained from teachers ratings on reading proficiency, math proficiency, reasoning ability and work organization. From parents they obtained ratings of general problems in school and academic performance in general. In addition, they had substantial information on the health of the child at birth and in early childhood.
Net of SES they found that for males the older the age of the mother at the birth of her first child the greater the reading proficiency, math proficiency, reasoning ability, and the fewer the school problems. For females, the older the age of mo
