In recent years, there have been considerable research advances regarding perinatal management, and the ability to explain prenatal as well as short and long-term post-natal Adverse outcomes, by using Placental pathology examination.  However, the value of this resource is still vastly under-utilized.

The Placenta is the Diary of Pregnancy

Any significant abnormal event during a pregnancy that can affect the baby, mother or both will most likely leave behind a discoverable “fingerprint.”  An expert pathology examination can identify morphologic changes that will substantiate the presence of abnormal acute or chronic intrauterine conditions that have caused, or in combination contributed to, an adverse pregnancy outcome.  Many of these adverse events are the result of either a missed or delayed diagnosis of otherwise treatable antenatal Maternal or fetal conditions.

The placenta is mostly of fetal origin.  However, there are also important maternal elements in the so-called basal plate and maternal decidua of the extraplacental membranes.  The maternal elements contain maternal decidual vessels, which bring maternal blood to the placenta for exchange of oxygen and nutrients with the fetus.  These vessels hold evidence of maternal conditions such as preeclampsia, hypertensive disorders, diabetes, etc., which can result in decreased uteroplacental perfusion.  Consequences of decreased uteroplacental perfusion range from slow growth (intrauterine growth restriction) to fetal death (stillbirth) in severe cases.

For instance: the mother may have had a high-risk obstetrical condition such as pre-eclampsia, or abruption.  Adverse outcomes could result if this condition was not appropriately evaluated, diagnosed and treated.  Placental evaluation can prove the presence of such conditions by showing evidence of maternal vascular malperfusion— a combination of morphologic alterations within both the fetal and maternal compartment of the placenta.

Litigation

One of the most common reasons for litigation is an uneventful pregnancy course, followed by an unexpected peripartum adverse outcome in a term infant.  One scenario is an infant unresponsive at birth with low Apgar scores, that requires resuscitation.  This scenario is commonly seen in children who later develop cerebral palsy and various types of neurologic injury, neurologic impairment, or developmental delays.

Placental lesions associated with adverse neurologic outcome can be divided into those with abnormal blood flow in the maternal circulation (maternal vascular malperfusion), abnormal blood flow in the fetal circulation (primarily fetal thrombotic vasculopathy), inflammatory processes (acute chorioamnionitis, chronic villitis/villitis of unknown etiology), and primary placental lesions.  Each of these is associated with well-defined identifiable pathologic alterations.  On the other hand, absence of such placental lesions on pathology examination speaks against significant prenatal intrauterine adverse conditions.  Thus negative findings on placental examination can also be used to support a case.

Intrauterine Growth Restriction

Intrauterine growth restriction is a common prenatal complication that is associated with serious adverse pregnancy outcomes including stillbirth, as well as long term disability.  Growth restriction is a significant risk factor for cerebral palsy.  Severe growth restriction has been associated with placental abnormalities as a result of maternal vascular malperfusion or diffuse chronic villitis, as well as entities such as massive perivillous fibrin deposition and chronic histiocytic perivillositis among others.  However, undiagnosed and improperly managed intrauterine growth restriction can be difficult to substantiate based on clinical evaluation alone.

Under normal conditions, one quarter to a third of the placenta may be rendered nonfunctional by such pathologic processes without a significant adverse effect on oxygen exchange.  However, when chronic processes have resulted in a placenta with little or no reserves, the infant is particularly susceptible to additional insults that may occur during labor and delivery.

Multiple Factors Acting Simultaneously

Many times the adverse pregnancy outcome is a result of several unfavorable factors acting simultaneously.  Intrauterine infection and its histologic counterpart in the placenta– acute chorioamnionitis– is common.  However most healthy fetuses will be able to fight the infection successfully without significant long term sequelae.  On the other hand, a fetus that has been already compromised by intrauterine growth restriction due to maternal vascular malperfusion will be a lot more likely to suffer serious consequences from a similar infection, even in the event of antibiotic therapy.

Duration and Approximate Timing of Pathologic Processes

Expert placental evaluation can furthermore estimate duration and approximate timing of pathologic processes in utero.  When under stress of any kind in utero, the fetus is likely to release meconium in the amniotic fluid which gets deposited within the placental membranes.  It is possible to estimate the duration of meconium exposure, and therefore approximate timing of noxious stimuli, by identifying the location of meconium-laden macrophages.  This is done by histologic examination of the fetal membranes.

Placentas of neurologically impaired infants often show multiple lesions.  The timing of these lesions can provide a ‘‘storyline’’ of events in the creation of an adverse intrauterine environment.  Multiple lesions of different etiologies, and involving different aspects of placental function (eg. fetal versus maternal blood circulation), can act synergistically to decrease placental reserves and function.  The same is true when acute events occur in combination with chronic processes.  The presence of multiple placental lesions greatly increases the susceptibility of the fetus to neurologic injury, as shown in recent studies.

The extent to which placental pathology can be helpful in understanding adverse antenatal and perinatal events varies with the type and significance of placental lesions.  Interpretation of these lesions is complex and requires experience and insight into clinicopathologic correlation with outcome.  However, the most important part of placental examination is ensuring that it is performed.  The diary of pregnancy should not be a secret anymore.

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