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 estimated.
The study, published today 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, which poses a greater risk of serious complications, such as breathing difficulties and infections. In contrast, the researchers found no evidence that caffeine intake affected fetal development.
Pregnant women, or even those who aspire to become pregnant, have long been advised to stop smoking and limit caffeine consumption due to the risk it poses to the unborn baby, because tobacco use has been associated with lower fetal growth, premature birth and low birth weight, and even with the likelihood of preeclampsia (high blood pressure during pregnancy).
But the studies that analyzed these links between smoking, caffeine and complications during pregnancy are mostly based on self-reported data, on what pregnant women say they consume.
The Cambridge researchers decided to look for a more objective measure of pregnant women's exposure to tobacco and caffeine by looking at levels of metabolites in the blood, the chemical residues created when the body processes substances such as tobacco and caffeine.
To evaluate exposure to cigarette smoke, they monitored cotinine levels by analyzing blood samples from 914 women taken four times during their pregnancy. And they found that those who had consistent exposure to smoking during pregnancy 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 1.27, less than half). In addition, they observed that they quadrupled the probability of experiencing fetal growth problems.
Specifically, according to the results of the research, the babies of smokers weighed on average 387 grams less than those of non-smoking mothers, which means more than 10% less than the average weight of a newborn, and the low weight at birth is associated with a higher risk of developmental problems and poorer health later in life.
On the other hand, as they explain in the note detailing their work, the researchers found no evidence that smoking affects the risk of preeclampsia.
"We have 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," said Gordon Smith, head of Obstetrics and Gynecology at the University of Cambridge. encourages pregnant women and women planning a pregnancy to access smoking cessation services so as not to put their baby at risk of serious complications from growing too slowly in the womb or being born too early.
"Pregnancy is a key time for women to quit smoking, and if they can remain smoke-free after giving birth, there will be lifelong benefits for themselves and their children," Smith said. In the case of Spain, some reports put the percentage of pregnant women who smoke at 20%.
Regarding the impact of caffeine intake, the researchers analyzed the presence of the metabolite paraxanthine in the analyzes of 915 pregnant women and found little evidence of an association between high levels suggesting high caffeine intake and adverse outcomes during pregnancy. pregnancy or childbirth.
