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Mums who smoke risk major birth defects in their babies

Risk particularly high for missing limbs, club foot, cleft lip and gastrointestinal deformities

Caroline White

Tuesday, 12 July 2011

Smoking during pregnancy is associated with several major birth defects, finds a large systematic review published online today in Human Reproduction Update.

The findings are based on 172 research papers published over the past 50 years, involving a combined total of 174,000 cases of birth defects and 11.7 million normal babies.

The researchers found that there was an increased risk of defects among babies whose mothers smoked during the pregnancy compared with those whose mothers did not smoke.

There were small increases in the risk of missing or deformed fingers and toes, undescended testes and musculoskeletal and cardiovascular defects of between 9 and 19%.

There was a much higher risk of between 25% and 50% of missing limbs, club foot, cleft lip/palate and gastrointestinal defects, including hernia and gastroschisosis, where parts of the stomach or intestines protrude through the skin.

It is not known for sure how smoking can contribute to this increased risk, but possible explanations include the vasoconstrictor action of nicotine on blood flow to the placenta and carbon monoxide binding to haemoglobin, effectively restricting the oxygen supply to placental and fetal tissues, say the authors.

Mothers who smoke, should be advised of the risks they are taking, urge the authors, who advocate that for those who simply cannot give up, nicotine replacement therapy may be an option.

In the UK 45% of women under 20 and 17%, overall, still smoke during pregnancy, according to figures from the Office for National Statistics (2006).

Commenting on the research, Basky Thilaganathan, spokesperson for the Royal College of Obstetricians and Gynaecologists, said: “It is well known that smoking increases the risk of preterm birth and low birthweight. This study shows that smoking also increases the risk of birth defects which can seriously affect a baby’s quality of life.”

She continued: “Pregnant women need to be informed of the risks of smoking during pregnancy and should be offered advice and support to help them give up. Women who are unable to quit smoking should be encouraged to reduce smoking as much as they can.”

Maternal smoking in pregnancy and birth defects: a systematic review based on 173,687 malformed cases and 11.7 million controls. Human Reproduction Update doi 10.1093/humupd/dmr022; published online July 12 2011

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