Trying to Understand Stillbirths

Stillbirths affects 1% of all pregnancies in US, amounting to nearly 24,000 deaths every year. Recent advances in medicine has brought down the neonatal and infant mortality considerably in last decade, but the decline is still birth rate is very slow.

A lack of understanding of the mechanisms behind it coupled with inability to predict stillbirth has prevented significant improvement in stillbirths’ rate.

Although altered fetal growth and placental abnormalities are strongest predictors of stillbirths but all patients with placental abnormalities do not end up in stillbirths, reflecting our lack of understanding of this interrelationship.

This population based case control study included 613 women who had stillbirths and 1747 women who had live births and who consented to placental pathological examination from 59 hospitals in 5 geographic areas in the U.S.

Study was published online August 18, 2017 in Journal PloS one.

About 15 placental pathologies were most prevalent in women with stillbirths and fetal growth abnormalities.

Out of 15, ten were also associated with fetal growth retardations. These are: single umbilical artery; velamentous insertion; terminal villous immaturity; retroplacental hematoma; parenchymal infarction; intraparenchymal thrombus; avascular villi; placental edema; placental weight; ratio birth weight/placental weight)

The other 5 (acute chorioamnionitis of placental membranes; acute chorioamionitis of chorionic plate; chorionic plate vascular degenerative changes; perivillous, intervillous fibrin, fibrinoid deposition; fetal vascular thrombi in the chorionic plate) resulted in stillbirths without altered fetal growth.  

Terminal villous hypoplasia was equally common in live born and still born fetuses with altered fetal growth.

Maternal factors associated with still births were gestational hypertension/pre-eclampsia (20% versus 11%, p<0.001), hypertension before pregnancy (11% versus 5%, p<0.001), and pregestational diabetes (7% versus 2%, p<0.001)

Fetal factors associated with still births were congenital malformations (13% versus 3%, p<0.001), lower birth weight (median 1,949 versus 3,321 grams, p<0.001), and lower GA (median 33 versus 39 weeks, p<0.001).

The study results suggest that different mechanisms exist for disruption in placental function and the results vary according to timing of gestation. An acute insult results in still births but no fetal growth alterations while a chronic, low level insult results in fetal growth retardation which may end up in still births.

Some of these placental findings can be diagnosed with prenatal ultrasound and pregnancies managed accordingly, Similarly, birth weight to placental weight ratio could be estimated antenatally by ultrasound and those pregnancies with abnormal ratio and at risk of stillbirths could benefit from early  term delivery.

Access the abstract, Full Text.