Researchers at the University of Cambridge have found that women who smoke during pregnancy are 2.6 times more likely to give birth prematurely than non-smokers, more than double what previous studies had estimated. Their study, published yesterday in the International Journal of Epidemiology, also found that when a pregnant woman smokes, the baby is four times more likely to be small for its gestational age, putting it at greater risk of serious complications, such as breathing difficulties and infections. Instead, they found no evidence that caffeine intake affects fetal development as previously believed.
Pregnant women, or even those aspiring to become pregnant, have long been advised to quit smoking because tobacco use has been associated with reduced fetal growth, premature birth and low birth weight , and even with the likelihood of preeclampsia (high blood pressure during pregnancy). There is also evidence that exposure of pregnant women to tobacco, even as passive smokers, increases the risk of neurodevelopmental alterations and results in worse long-term neurological outcomes.
But the studies that analyze these links between smoking and complications during pregnancy are mostly based on self-reported data, on what pregnant women say that they smoke, and gynecologists know that a high percentage smoke secretly or relativize their consumption of tobacco “Despite all that is known about their damage to fetal development, there is still a high consumption of tobacco and alcohol during pregnancy and many women who do not know that only two cigarettes also count, that every puff they take makes the fetus”, emphasizes the director of BCNatal, specialist in pregnancy and fetal disease.
Because of all this, the Cambridge researchers decided to look for a more objective measure of the actual exposure of pregnant women to tobacco and caffeine by looking at the levels of metabolites in the blood, the chemical residues that are created when the body processes tobacco and caffeine.
To assess exposure to cigarette smoke, they monitored cotinine levels in blood samples from 914 women taken four times during pregnancy. And they found that those who showed consistent exposure to secondhand smoke were 2.6 times more likely to experience spontaneous preterm birth than those who were not exposed (the previous estimate from a meta-analysis of studies was d ‘1.27, less than half). In addition, they observed that they were four times more likely to experience fetal growth problems. Specifically, the babies of smokers weighed an average of 387 grams less than those of non-smokers, which means more than 10% less than the average weight of a newborn, and low birth weight is related to a higher risk of developmental problems and poorer health in the future. In contrast, they found no evidence that smoking affects the risk of preeclampsia.
“We’ve known for a long time that smoking during pregnancy is not good for the baby, but our study shows that it is much worse than previously thought,” explained the University of Cambridge’s Head of Obstetrics and Gynecology, Gordon Smith, who encourages pregnant women and women planning pregnancy to quit smoking so as not to put their baby at risk of serious complications from growing too slowly in the womb or being born too early.
Regarding the impact of caffeine, the researchers analyzed the presence of the metabolite paraxanthine and found little evidence of an association between high caffeine intake and adverse outcomes during pregnancy or childbirth. Gratacós says that this is one of the most significant results for perinatal health specialists. “Other studies linked poor perinatal outcomes to caffeine consumption, but this research – which is very well done – shows that coffee is a confounding variable, that when you control and adjust for others (such as whether the mother smokes or the type of life you lead), it turns out that caffeine is not associated with a greater risk”, he explains.
