Cambridge researchers have found that women who smoke during pregnancy are 2.6 times more likely to give birth prematurely compared to non-smokers – more than double the previous estimate.
The study, published today in the International Journal of Epidemiology, also found that smoking meant that the baby was four times more likely to be small for its gestational age, putting it at risk of potentially serious complications including breathing difficulties and infections.
But the team found no evidence that caffeine intake was linked to adverse outcomes.
Women are currently recommended to stop smoking and limit their caffeine intake during pregnancy because of the risk of complications to the baby. For example, smoking during pregnancy is associated with an increased risk of fetal growth restriction, premature birth and low birthweight, though it has also been linked to a reduced risk of preeclampsia (high blood pressure during pregnancy).
High caffeine intake has also been shown to be associated with lower birthweights and possibly fetal growth restriction. Caffeine is more difficult to avoid than cigarette smoke as is found in coffee, tea, chocolate, energy drinks, soft drinks, and certain medications.
Studies looking at the links between smoking, caffeine and adverse pregnancy outcomes tend to rely on self-reported data to estimate exposure, which is not always reliable. A more objective measure is to look at levels of metabolites in the blood – chemical by-products created when substances such as tobacco and caffeine are processed in the body.
Researchers at the University of Cambridge and the Rosie Hospital, part of Cambridge University Hospitals NHS Foundation Trust, recruited more than 4,200 women who attended the hospital between 2008 and 2012 as part of the Pregnancy Outcome Prediction (POP) study. The team analysed blood samples taken from a subset of these women four times during their pregnancies.
Cambridge Reproduction member Professor Gordon Smith, Head of the Department of Obstetrics and Gynaecology at the University of Cambridge, said: “We’ve known for a long time that smoking during pregnancy is not good for the baby, but our study shows that it’s potentially much worse than previously thought. It puts the baby at risk of potentially serious complications from growing too slowly in the womb or from being born too soon.
“We hope this knowledge will help encourage pregnant mums and women planning pregnancy to access smoking-cessation services. Pregnancy is a key time when women quit and if they can remain tobacco free after the birth there are lifelong benefits for them and their child.”
Reference
Selvaratnam, RJ et al. Objective measures of smoking and caffeine intake and the risk of adverse pregnancy outcome. International Journal of Epidemiology; 28 Sept 2023; DOI: 10.1093/ije/dyad123
Adapted from a press release on the University of Cambridge website.