Most smokers realise it's not a good idea to smoke around women who are pregnant. And now there's even more evidence to suggest why exposing pregnant women to tobacco smoke can harm their babies.
According to experts from the University of Nottingham, passive smoking during pregnancy increases the risk of still birth by almost a quarter. Pregnant non-smokers who breathe in other people's cigarette smoke could also have a 13% higher chance of having a baby with birth defects, they claim.
The study, published in the journal Pediatrics, suggest it's not enough to persuade women to give up smoking when they're pregnant. You've got to get their partners to quit too, claim the researchers.
"Smoking during pregnancy carries a range of serious health risks for the unborn baby including fetal mortality, low birth weight, premature birth and a range of serious birth defects such as cleft palate, club foot and heart problems," says Dr Jo Leonardi-Bee.
"Since passive smoking involves exposure to the same range of tobacco toxins experienced by active smokers, albeit at lower levels, it is likely that coming into contact with second-hand smoke also increases the risk of some or all of these complications."
Women should avoid passive smoking before pregnancy as well as during, the researchers add, since it's not clear when the negative effects of second-hand smoke begin. Men should also quit smoking before trying for a baby, since smoking has an impact on sperm development, they claim.
Being exposed to ten or more cigarettes a day is all it takes for the risks to be increased, say the scientists.
Have you quit smoking recently?