Research adds insight on stillbirth risk factors



Stillbirth is a major public health problem, occurring in approximately 1 of every 160 pregnancies in the United States. The rate has remained stagnant since 2006. Prior to that time, from 1990 to 2006, the rate declined somewhat, but only half as much as the decline in infant mortality during this time period. Racial disparities also have persisted, with non-Hispanic black women having more than a twofold increase in risk (Natl Vital Stat Rep. 2012;60:1-22).

Research conducted by the Stillbirth Collaborative Research Network (SCRN) and others has provided us with insight on risk factors and on probable and possible causes of death among stillbirths, which are defined as fetal deaths at 20 or more weeks’ gestation. We know from SCRN data, for instance, that black women are more likely to have stillbirths associated with obstetric complications and infections than white and Hispanic women. However, we still cannot explain a substantial proportion of stillbirths, despite a complete evaluation, or predict who will have a stillbirth.

Dr. Uma M. Reddy

Dr. Uma M. Reddy

What we can do as obstetricians is be aware that stillbirth is one of the most common adverse pregnancy outcomes in the United States and counsel women regarding risk factors that are modifiable. Moreover, when stillbirth happens, a complete postmortem evaluation that includes autopsy, placental pathology, karyotype or microarray analysis, and fetal-maternal hemorrhage testing is recommended (Obstet Gynecol. 2009;113[3]:748-61). Recent data show that each of these four components is valuable and should be considered the basic work-up for stillbirth.

Risks and causes

Pregnancy history was the strongest baseline risk factor for stillbirth in an analysis of 614 stillbirths and 1,816 live births in the SCRN’s population-based, case-control study conducted between 2006 and 2008. The SCRN was initiated by the Eunice Kennedy Shriver National Institute of Child Health and Human Development in 2003. This critical population-based study was conducted at 59 U.S. tertiary care and community hospitals in five catchment areas and has been analyzed in more than 15 published reports.

Women with a previous stillbirth have been known to be at 5- to 10-fold increased risk of a recurrence of stillbirth, and the SCRN findings confirmed this. The study added to our knowledge, however, with the finding that even a prior pregnancy loss at less than 20 weeks’ gestation increased the risk for stillbirth.

Other risk factors identified in the study, in addition to race, included having a multifetal pregnancy (adjusted odds ratio of 4.59), diabetes (AOR of 2.50), maternal age of 40 years or older (AOR of 2.41), maternal AB blood type (AOR of 1.96, compared with type O), a history of drug addiction (AOR of 2.08), smoking during the 3 months prior to pregnancy (AOR of 1.55-1.57, depending on amount), and being unmarried and not cohabitating (AOR of 1.69). Regarding racial disparity, the study showed that elevated risk of stillbirth for non-Hispanic blacks occurred predominantly prior to 24 weeks of gestation.

As in prior research, overweight and obesity also conferred elevated risks in the SCRN study (AORs of 1.43 and 1.72, respectively), and these risks were not explained by either diabetes or hypertension (JAMA. 2011;306:2469-79).

The use of assisted reproductive technology was not included in the study’s multivariate model, but previous research has shown a fourfold increased risk of stillbirth for singleton IVF/ICSI pregnancies. The reason is unclear, but the risk appears to be more related to IVF/ICSI rather than the underlying infertility (Hum Reprod. 2010 May;25[5]:1312-6).

A previous preterm or small-for-gestational-age birth has also been shown in prior research to be a significant risk factor for stillbirth. Less clear is the role of previous cesarean delivery in stillbirth risk. An association has been demonstrated in several studies, however, including one involving about 180,000 singleton pregnancies of 23 or more weeks’ gestation. Women in this cohort who had a previous cesarean delivery had a 1.3-fold increased risk of antepartum stillbirth, after controlling for important factors such as race, body mass index (BMI), and maternal disease (Obstet Gynecol. 2010 Nov;116[5]:1119-26).

In another analysis of the SCRN study looking specifically at causes of stillbirth, a “probable” cause of death was found in 61% of cases and a “possible or probable” cause of death in more than 76% of cases. The most common causes were obstetric complications (29.3%), placental abnormalities (23.6%), fetal genetic/structural abnormalities (13.7%), infection (12.9%), umbilical cord abnormalities (10.4%), hypertensive disorders (9.2%), and other maternal medical conditions (7.8%).

A higher proportion of stillbirths in non-Hispanic black women, compared with non-Hispanic white women and Hispanic women was associated with obstetric complications (43.5%) and infections (25.2%). This finding combined with the finding that stillbirth in black women often occurs at less than 24 weeks’ gestation suggests that measures aimed at reducing the rate of spontaneous preterm birth in black women could potentially reduce the rate of stillbirth as well (JAMA. 2011 Dec 14;306[22]:2459-68).

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