Risks of stillbirth and neonatal death with advancing gestation at term: A systematic review and meta-analysis of cohort studies of 15 million pregnancies

Abstract

Background

Despite advances in healthcare, stillbirth rates remain relatively unchanged. We conducted a systematic review to quantify the risks of stillbirth and neonatal death at term (from 37 weeks gestation) according to gestational age.

Methods and findings

We searched the major electronic databases Medline, Embase, and Google Scholar (January 1990–October 2018) without language restrictions. We included cohort studies on term pregnancies that provided estimates of stillbirths or neonatal deaths by gestation week. We estimated the additional weekly risk of stillbirth in term pregnancies that continued versus delivered at various gestational ages. We compared week-specific neonatal mortality rates by gestational age at delivery. We used mixed-effects logistic regression models with random intercepts, and computed risk ratios (RRs), odds ratios (ORs), and 95% confidence intervals (CIs). Thirteen studies (15 million pregnancies, 17,830 stillbirths) were included. All studies were from high-income countries. Four studies provided the risks of stillbirth in mothers of White and Black race, 2 in mothers of White and Asian race, 5 in mothers of White race only, and 2 in mothers of Black race only. The prospective risk of stillbirth increased with gestational age from 0.11 per 1,000 pregnancies at 37 weeks (95% CI 0.07 to 0.15) to 3.18 per 1,000 at 42 weeks (95% CI 1.84 to 4.35). Neonatal mortality increased when pregnancies continued beyond 41 weeks; the risk increased significantly for deliveries at 42 versus 41 weeks gestation (RR 1.87, 95% CI 1.07 to 2.86, p = 0.012). One additional stillbirth occurred for every 1,449 (95% CI 1,237 to 1,747) pregnancies that advanced from 40 to 41 weeks. Limitations include variations in the definition of low-risk pregnancy, the wide time span of the studies, the use of registry-based data, and potential confounders affecting the outcome.

Conclusions

Our findings suggest there is a significant additional risk of stillbirth, with no corresponding reduction in neonatal mortality, when term pregnancies continue to 41 weeks compared to delivery at 40 weeks.

Systematic review registration

PROSPERO CRD42015013785

Abstract

Javaid Muglu and colleagues reveal the increasing risk of stillbirths and neontatal deaths for pregnancies that go beyond 41 weeks.

Author summary

Why was this study done?

• A third of stillborn babies in the UK are born at term (>37 weeks) and were previously considered to be healthy.

• Prolongation of pregnancy at term is a known risk factor for stillbirth. Currently women are routinely offered induction of labour after 41 weeks gestation to avoid stillbirth. But 1 in 3 women have a stillborn baby prior to this gestational age.

• Mothers need robust estimates of potential risks of stillbirth and newborn death at term to make decisions on timing of delivery.

What did the researchers do and find?

• We collated data from all relevant studies found in a systematic review and determined the additional risks of stillbirth and newborn death in mothers at term gestation, by comparing pregnancies that continued versus delivered at various gestational ages,.

• We found a steady increase in the risk of stillbirth with advancing gestation at term. In mothers who continued their pregnancy to 41 weeks, there was a 64% increase in the risk of stillbirth compared to those who delivered at 40 weeks, with 1 additional mother having a stillborn baby for every 1,449 women.

• The risks of newborn death remained constant between 38 and 41 weeks, and only increased beyond 41 weeks.

What do these findings mean?

• Any mother considering prolongation of pregnancy beyond 37 weeks should be informed of the additional small but significantly increased risk of stillbirth with advancing gestation.

• Women planning delivery before 41 weeks gestation can be reassured that there is no additional risk of newborn death when delivering between 38 and 41 weeks.

• Our findings are limited by variations in the definition of low-risk pregnancy, the inclusion of studies over a long period of time, and the possibility of other unaccounted factors that may have affected the outcomes.