Factors Associated with Occurrence of Stillbirth before 32 Weeks of Gestation in a Contemporary Cohort

Abstract

Objective: We sought to quantify the distribution of stillbirths by gestational age (GA) in a contemporary cohort and to determine identifiable risk factors associated with stillbirth prior to 32 weeks of gestation.

Study design: Population-based case-control study of all stillbirths in the United States during the year 2014, utilizing vital statistics data, obtained from the National Center for Health Statistics. Distribution of stillbirths were stratified by 20 to 44 weeks of GA, in women diagnosed with stillbirth in the antepartum period. Pregnancy characteristics were compared between those diagnosed with stillbirth <32 versus ≥32 weeks of gestation. Multivariate logistic regression estimated the relative influence of various factors on the outcome of stillbirth prior to 32 weeks of gestation.

Results: There were 15,998 nonlaboring women diagnosed with stillbirth during 2014 in the United States between 20 and 44 weeks. Of them, 60.1% (n = 9,618) occurred before antenatal fetal surveillance (ANFS) is typically initiated (<32 weeks) and 39.9% (n = 6,380) were diagnosed at ≥32 weeks. Women with stillbirth prior to 32 weeks were more likely to be of non-Hispanic Black race (29.0 vs. 23.9%, p < 0.001), nulliparous (53.8 vs. 50.6%, p = 0.001), have chronic hypertension (CHTN; 6.0 vs. 4.3%, p < 0.001), and fetal growth restriction as evidenced by small for GA (SGA < 10th%) birth weight (44.8 vs. 42.1%, p < 0.001) as opposed to women with stillbirth after 32 weeks. After adjustment, SGA birth weight (adjusted odds ratio [aOR] = 1.2, 95% confidence interval [CI]: 1.1-1.3), Black race (aOR = 1.2, 95% CI: 1.1-1.3), and CHTN (aOR = 1.3, 95% CI: 1.1-1.5) were associated with stillbirth prior to 32 weeks of gestation as opposed to stillbirth after 32 weeks.

Conclusion: More than 6 out of 10 stillbirths in this study occurred <32 weeks of gestation, before ANFS is typically initiated under American College of Obstetricians and Gynecologists recommendations. Among identifiable risk factors, CHTN, Black race, and fetal growth restriction were associated with higher risk of stillbirth before 32 weeks of gestation. Earlier ANFS may be warranted at in certain "at risk" women.

Key points: · Six out of 10 stillbirths occur before 32 weeks of gestation.. · We evaluated factors associated with stillbirth <32 weeks.. · Hypertension and fetal growth restriction were associated with early stillbirth..