Study shows increasing stillbirth risk of moms-to-be who smoke, drink

Women who drank alcohol and smoked during pregnancy had an almost three times higher risk of stillbirth compared with women who completely abstained from these behaviours.

Experts at Stellenbosch University (SU) involved in a new international study found that the combined effect of drinking and smoking in pregnancy compounded the risk for stillbirth and Sudden Infant Death Syndrome (Sids).

Between 2007 and 2015, the study followed the drinking and smoking behaviour of nearly 12 000 South African and American women during pregnancy, and collated the results with their pregnancy outcomes.

Smoking alone had a relative risk of 1.6 for stillbirth, while drinking alone had a relative risk of 2.2. This risk increased when these behaviours continued beyond the first trimester of pregnancy.

The study also found a 12 times higher risk for Sids in cases where women drank and smoked during pregnancy. In cases where the women drank but did not smoke, the risk for Sids increased by four, and when they smoked but did not drink, there was a five times higher chance for Sids.

Professor Hein Odendaal of SU’s Obstetrics and Gynaecology department, who led the South African chapter of the Safe Passage Study, said this was the first study to show that combining these risk factors strengthened the negative effects on stillbirths and Sids.

“What’s particularly alarming is that these behaviours were quite common among study participants. More than half used alcohol (52.3%) sometime during pregnancy, and 17% continued drinking throughout the entire pregnancy.

“Almost half of them smoked (49%) sometimes during pregnancy, and a third (33%) continued smoking for the duration of the pregnancy,” Odendaal said.

The study was funded by the National Institutes of Health in the US, and followed the pregnancies of 11892 women from the first prenatal visit to the child’s first year of life.

According to Odendaal, earlier studies on drinking and/or smoking during pregnancy only collected data after delivery, relying on the mother’s memory of events.

“This study is unique in that we collected data throughout the pregnancy, which we collated with health data from the mother, foetus and later also the infant,” Odendaal said.

Up to three assessments were done on the mother and foetus during pregnancy, and after delivery, another three assessments were done on the infant – at birth, at one month of age, and at one year.

The researchers found that drinking and smoking reduced blood flow in the uterine and umbilical arteries, two of the main vessels involved in foetal nutrition and growth, as early as 20-24 weeks of gestation. Even low levels of drinking and smoking affected blood flow in the umbilical artery, Odendaal said.

The study also found an association between smoking and placental insufficiency – a complication of pregnancy where the placenta is unable to deliver an adequate supply of nutrients and oxygen to the foetus, and can’t fully support the developing baby.

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