Research has shown that drinking and smoking during pregnancy slows foetal development, and may cause severe harm and even death to the foetus.
A new study, conducted jointly in South Africa and the United States, has revealed more shocking findings.
Almost 12 000 pregnant women participated in the Safe Passage Study between 2007 and 2015. The study followed the smoking and drinking behaviour of these women. The data was then analysed with their pregnancy outcomes.
Researchers discovered that those women who drank alcohol and smoked during their pregnancies were at almost three times higher risk of experiencing stillbirth during the course of their pregnancies than women who did not drink.
Researchers also found that drinking and smoking during pregnancy 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.
Combination of smoking and drinking
Professor Hein Odendaal of the Department of Obstetrics and Gynaecology at Stellenbosch's Faculty of Medicine and Health Science (FMHS) led the South African division of the study.
In a statement, Odendaal said that this was the first study to show that combining these risk factors increased the risk of stillbirths and sudden infant death syndrome (SIDS).
"Even low levels of drinking and smoking affected blood flow in the umbilical artery. Higher levels of smoking and drinking aggravated these effects on blood flow," said Odendaal.
Trauma to the placenta
The study also discovered a link between smoking and placental insufficiency, a pregnancy complication which happens when the placenta is unable to deliver an adequate supply of nutrients and oxygen to the foetus and cannot fully support the developing baby.
Odendaal added that preterm birth and placental abruption – the separation of the placenta from the uterine lining, which is potentially fatal for both foetus and mother – are two of the main causes of stillbirth in South Africa. Smoking, and now the combination of smoking and drinking, are known risk factors for both conditions.
Smoking carried a 1.6-fold risk for stillbirth, and drinking a relative risk of 2.2, but when pregnant women continued smoking and drinking past the first trimester of pregnancy (12 weeks), the risk increased.
High SIDS risk
The study also discovered that there is a 12 times higher risk of SIDS, even when women smoked and did not drink, or vice versa.
"What's particularly alarming is that these behaviours were quite common among study participants. More than half used alcohol at some time during pregnancy (52.3%) and some continued drinking throughout their pregnancy (17%).
"Almost half of them smoked at some stage during their pregnancy (49%) and a third continued smoking for the duration of the pregnancy," added Odendaal.
Largest study of its kind
South Africa provided the bulk of the study participants (59.1%) and America carried the remaining 40.9%.
Odendaal added that there has never been such a large prospective study looking at the use of alcohol and tobacco in pregnancy is such detail.
"Earlier studies on drinking and/or smoking during pregnancy only collated 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," said Odendaal.
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.
Several factors taken into consideration
Researchers noted several factors which contributed to an increase in stillbirth risk. They noted that stillbirths were more common in the South African division of the study than the American division.
They also noted that the level of education played a significant role. Fewer years of schooling were associated with a higher risk of stillbirth.
The length of pregnancy (premature delivery) and restricted growth during pregnancy also contributed to a higher risk of stillbirth.