Smoking during pregnancy may cause birth defects

A study has found that smoking during pregnancy can lead to common birth defects like missing or deformed limbs, clubfoot, facial disorders and gastrointestinal problems.

The study by scientists at UCL is the first comprehensive review to identify the specific birth defects (malformations) most associated with smoking.

The authors examined a total of 172 research papers published over the last 50 years, which looked at a combined total of 174,000 cases of malformation alongside 11.7 million controls.

The risk was increased by 26 per cent for having a baby with missing or deformed limbs, 28 per cent for clubfoot, 27 per cent for gastrointestinal defects, 33 per cent for skull defects, 25 per cent for eye defects, and 28 per cent for cleft lip/palate.

The greatest increase in risk (50 per cent) was for a condition called gastroschisis, where parts of the stomach or intestines protrude through the skin.

The research authors recommend that public health guidance should now be more explicit about the specific malformations associated with maternal smoking, in order to try and reduce the numbers of pregnant women who smoke.

"People may think that few women still smoke when pregnant," lead author professor Allan Hackshaw, UCL Cancer Institute and member of the Royal College of Physicians Tobacco Advisory Group, said. 

"But the reality is that, particularly in women under 20, the numbers are still staggeringly high. "Maternal smoking during pregnancy is a well established risk factor for miscarriage, low birth weight and premature birth.

"However, very few public health educational policies mention birth defects when referring to smoking and those that do are not very specific - this is largely because of past uncertainty over which ones are directly linked.

"Now we have this evidence, advice should be more explicit about the kinds of serious defects such as deformed limbs  and facial and gastrointestinal malformations that babies of mothers who smoke during pregnancy could suffer from.

"The message from this research is that women should quit smoking before becoming pregnant, or very early on, to reduce the chance of having a baby with a serious and lifelong physical defect," Hackshaw added.

The study has been published in Human Reproduction Update.