Women who smoke during pregnancy are 2.6 times more likely to give birth prematurely than non-smokers, almost double previous estimates.

In a new study, researchers at the University of Cambridge showed that smoking during pregnancy is linked to premature birth and low birth weights. Babies born to mothers who smoked throughout their pregnancy were four times more likely to be small for their gestational age, which can lead to serious complications, including breathing difficulties and infections.

The findings are published in the International Journal of Epidemiology, and researchers hope they will encourage more pregnant women to seek help from smoking cessation services available within the NHS.

On exposure to cigarette smoke, levels of the metabolite cotinine will be elevated in the blood, urine and saliva; for caffeine analysis, the metabolite paraxanthine was measured.

Of the 914 women who smoked, 78.6 per cent were shown to have no exposure to cotinine during pregnancy. 11.7 per cent had some exposure, and 9.7 per cent had consistent exposure throughout their pregnancy. Compared to non-smokers, the women who were consistently exposed to smoke were 2.6 times more likely to experience spontaneous premature birth, more than double the previous estimate of 1.27 from a meta-analysis study.

Consistent smokers were also 4.1 times more likely to experience fetal growth restriction. Babies of smokers were, on average, 387 grams lighter than those of non-smokers at birth, more than ten per cent smaller than the weight of the average newborn. A low birth rate is associated with an increased risk of developmental problems and poorer health in later life.

The researchers could not find any evidence to suggest that smoking was associated with a lower risk of preeclampsia, and they also found little association with caffeine intake and adverse outcomes at birth.

Professor Gordon Smith, from 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. We hope this knowledge will help encourage pregnant mums and women planning pregnancy to access smoking-cessation services.’

This article first appeared on our sister title Nursing in Practice.