Alcohol and tobacco use throughout the first trimester of pregnancy was associated with nearly 3 times the risk of late stillbirth (at 28 or more weeks), compared to women who neither drank alcohol nor smoked during pregnancy or quit both before the end of the first trimester.
The study, published in JAMA Network Open, was conducted to examine how smoking combined with alcohol use might further increase stillbirth risk.
Researchers in the Prenatal Alcohol in SIDS and Stillbirth (PASS) Network conducted the study, which was funded by the National Institutes of Health’s (NIH) Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD), National Institute on Alcohol Abuse and Alcoholism (NIAAA), and National Institute on Deafness and Other Communication Disorders (NIDCD).
Prenatal smoking is a known modifiable risk factor for stillbirth, but this study sought to uncover whether the combination of prenatal smoking and drinking played a role.
The prospective cohort study collected data between August 1, 2007, and January 31, 2015. Pregnant women from Cape Town, South Africa, and the Northern Plains of the US were recruited and followed up with throughout pregnancy. The main outcomes were stillbirth, defined as fetal death at 20 or more weeks’ gestation, and late stillbirth, defined as fetal death at 28 or more weeks’ gestation.
Of 11,663 pregnancies (mean [SD] gestational age at enrollment, 18.6 [6.6] weeks) in 8,506 women for whom the pregnancy outcome was known by 20 weeks’ gestation or later and who did not terminate their pregnancies, there were 145 stillbirths (12.4 per 1,000 pregnancies) and 82 late stillbirths (7.1 per 1,000 pregnancies).
In 51% of pregnancies, women reported no alcohol or tobacco cigarette exposure (risk of stillbirth, 4 per 1000 pregnancies). After the first trimester, 18% drank and smoked (risk of stillbirth, 15 per 1000 births), 9% drank only (risk of stillbirth, 10 per 1000 pregnancies), and 22% smoked only (risk of stillbirth, 8 per 1000 pregnancies). Compared with the reference group (pregnancies not prenatally exposed or without any exposure after the first trimester), the adjusted relative risk of late stillbirth was 2.78 (98.3% CI, 1.12-6.67) for pregnancies prenatally exposed to drinking and smoking, 2.22 (98.3% CI, 0.78-6.18) for pregnancies prenatally exposed to drinking only after the first trimester, and 1.60 (98.3% CI, 0.64-3.98) for pregnancies prenatally exposed to smoking only after the first trimester. The adjusted relative risk for all stillbirths was 1.75 (98.3% CI, 0.96-3.18) for dual exposure, 1.26 (98.3% CI, 0.58-2.74) for drinking only, and 1.27 (98.3% CI, 0.69-2.35) for smoking only compared with the reference group.
Women who drank and smoked through the first trimester and beyond had 2.78 times the risk for late stillbirth. Previously, the PASS Network also found that the risk of SIDS was 12 times higher in pregnancies exposed to maternal drinking and smoking past the first trimester.