Smoking during pregnancy doubles premature birth risk

Impact of smoking and caffeine on pregnancy outcomes.


Smoking during pregnancy has long been associated with adverse maternal and fetal outcomes. However, a recent study at the University of Cambridge has shed new light on the extent of the risk posed by smoking during pregnancy, revealing that it more than doubles the previous estimates of the likelihood of premature birth.

A new study in the International Journal of Epidemiology found that if a pregnant woman smokes, her baby is more likely to be smaller than expected when born. This can lead to severe problems like trouble breathing and infections for the baby. However, the study did not show that caffeine had the same effect.

Doctors usually tell pregnant women to stop smoking and not have too much caffeine because these things can harm the baby. Smoking during pregnancy can make the baby grow too slowly, be born too early, or be too small. But it might also have a smaller chance of causing high blood pressure in the mother during pregnancy.

Too much caffeine can also make babies weigh less when they’re born and possibly make them grow too slowly. Caffeine is in coffee, tea, chocolate, energy drinks, sodas, and medicines.

Most studies about smoking, caffeine, and pregnancy rely on what people say they do, which might not always be completely accurate. However, this study used a more reliable method by looking at the chemicals left in the blood when the body processes things like tobacco and caffeine.

Researchers from the University of Cambridge and the Rosie Hospital studied over 4,200 pregnant women between 2008 and 2012 as part of the Pregnancy Outcome Prediction (POP) study. They examined blood samples from some of these women four times during their pregnancies.

To understand if women were exposed to cigarette smoke, they checked for a substance called cotinine in their blood. This helps to determine if someone has been around cigarette smoke, even if they didn’t admit to smoking. Out of all the women in the study, only two out of three with cotinine in their blood said they smoked, proving that this is a more accurate way to check if someone smokes.

In their research about smoking, they looked at 914 women. About 78.6% of them didn’t have any exposure to smoking while pregnant, 11.7% had some direction, and 9.7% were consistently exposed to smoking.

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 suitable for the baby, but our study shows that it’s potentially much worse than previously thought. It puts the baby at risk of potentially severe complications from growing too slowly in the womb or 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.” He added

Pregnant women smoking were 2.6 times more likely to have their babies born too early, much higher than expected. These babies were also 4.1 times more likely to be smaller than usual.

Babies born to moms who smoked were about 387 grams lighter on average compared to babies born to moms who didn’t smoke. That’s more than 10% lighter than the usual weight for a newborn. Being born with such low weight increases the chances of having problems while growing up and poorer health later in life.

But unlike some past studies, this study didn’t find any proof that smoking lowers the chances of pre-eclampsia during pregnancy.

Pregnant women are routinely offered help to quit smoking, and local services are available for everyone, not just pregnant women. You can find more information on the NHS website.

To check how much caffeine these women had, the researchers looked at a substance called paraxanthine, which is a big part of how our bodies handle caffeine. They found that 12.8% of the women had low levels of paraxanthine, which means they likely had low caffeine intake. About 74% had moderate levels, and 13.2% had high paraxanthine levels. However, they didn’t find much proof that caffeine significantly affected the problems they studied.

This research was supported by the National Institute for Health and Care Research (NIHR) Cambridge Biomedical Research Centre and the Medical Research Council.

In conclusion, this study has highlighted the substantial risk that smoking during pregnancy poses concerning premature birth. The finding that this risk is more than double previous estimates emphasizes the critical importance of addressing smoking cessation during pregnancy to protect mothers’ and babies’ health. This research underscores the need to continue reducing smoking rates among pregnant individuals and promoting healthier pregnancies.

Journal Reference:

  1. Roshan J Selvaratnam, Ulla Sovio, et al., Objective measures of smoking and caffeine intake and the risk of adverse pregnancy outcomes. International Journal of Epidemiology. DOI: 10.1093/ije/dyad123.
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