More than double the previous estimate, researchers have shown that pregnant smokers are 2.6 times more likely to deliver a child early than pregnant non-smokers.
The research at Cambridge University revealed that smoking increased a baby's risk of being tiny for gestational age by four times, putting it at risk for potentially life-threatening conditions like infections and breathing problems.
The findings, published in the International Journal of Epidemiology, did not discover proof that caffeine use was connected to negative results.
Because of the possibility of difficulties for the unborn child, it is currently advised that pregnant women give up smoking and consume less caffeine. For instance, smoking during pregnancy has been linked to a lower risk of preeclampsia but is connected with an increased risk of fetal growth restriction, premature birth, and low birth weight.
A high caffeine intake is also linked to lower birth weights and fetal growth limitation. Since it is present in coffee, tea, chocolate, energy drinks, soft drinks, and some pharmaceuticals, caffeine is more difficult to avoid than cigarette smoke.
Studies examining the relationship between coffee, smoking, and unfavorable pregnancy outcomes frequently use unreliable self-reported data to assess exposure. Analyzing the amount of metabolites in the blood produced when the body metabolizes drugs like caffeine and tobacco provides a more accurate measurement.
How was the study examined?
More than 4,200 women who visited the hospital between 2008 and 2012 were recruited by researchers at the University of Cambridge and the Rosie Hospital, a division of Cambridge University Hospitals NHS Foundation Trust, for the Pregnancy Outcome Prediction (POP) study. Four times during each of these women's pregnancies, the team examined blood samples taken from a selection of these women.
The scientists examined levels of the cotinine metabolite, which may be found in blood, urine, and saliva, to gauge exposure to cigarette smoke. This metric is a more objective technique to evaluate smoking behavior because only two out of three women had measurable cotinine levels in each blood sample.
The analysis of smoking included a total of 914 women. Among these, 78.6% had no history of smoking while pregnant, 11.7% had some history, and 9.7% had regular exposure.
Smoking during pregnancy increased a woman's risk of spontaneous preterm birth by 2.6 times compared to a woman who did not smoke.
The average neonatal weight of babies born to smokers was 387g lower than that of newborns born to non-smokers, or more than 10% less. Due to this, there is a higher chance that the baby may be underweight, which is connected to a higher case of developmental issues and lower long-term health.
The team could not discover proof that smoking decreased the risk of preeclampsia, in contrast to earlier studies.
"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."- Professor Gordon Smith, University of Cambridge
He concludes: "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."
- International Journal of Epidemiology. Objective measures of smoking and caffeine intake and the risk of adverse pregnancy outcomes.
- University of Cambridge. Risk of premature birth from smoking while pregnant more than double previous estimates.
- NHS. Foods to avoid in pregnancy.