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Monday, 7 January, 2002, 12:35 GMT
Cannabis 'stunts baby growth'
Cannabis is not recommended during pregnancy
Women who smoke cannabis during pregnancy may be stunting the growth of their babies, research suggests.

The effect of one smoking one cannabis joint a week throughout pregnancy appears to be equivalent to the effect produced by smoking up to 15 cigarettes a day.

A team of researchers from the UK and New Zealand found no evidence that smoking cannabis when pregnant increases the risk of miscarriage.

But they did find that regular users were more likely to give birth to small babies.

However, the effect was small. On average, the babies of women who used cannabis at least once a week before and throughout pregnancy were 216g lighter than those of non-users.

They were also significantly shorter, and had smaller heads.

Once the researchers had taken into account other factors, such as cigarette smoking, they calculated that regular use of cannabis during pregnancy reduced average birth weight by an average of 90g.


Writing in the British Journal of Obstetrics and Gynaeocology, the researchers say: "These findings suggest that it would be prudent to advise pregnant women of the evidence that cannabis use may lead to reduced foetal growth.

"More generally, pregnant women should be encouraged to avoid all forms of substance use behaviour during pregnancy."

The reason why cannabis retards growth is still unclear. However, smoking the drug mixed with tobacco releases a cocktail of toxic chemicals that are thought likely to have a negative effect on the developing foetus.

The researchers studied more than 12,000 women expecting single babies.

Their work is part of an on-going project called the 'Children of the 90s' study, being coordinated at Bristol University.

Around one in 20 women who took part in the study admitted using cannabis before pregnancy, and a slightly smaller proportion said they used it while they were pregnant.

However, the researchers say that it is likely that this figure underestimates the true figure.

See also:

05 Jul 01 | Health
Cannabis 'not medical panacea'
13 Apr 01 | Health
Drug could block cannabis 'high'
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