With the British change in status of cannabis from a class A to class B drug, it became important to assess whether it is entirely safe for use during pregnancy.

A marker which often indicates an effect on the unborn child is the baby`s weight at birth.

The findings were announced by Kate Northstone, from the Children of the 90s project, also known as ALSPAC (Avon Longitudinal Study of Parents and Children). This study, based in Bristol, has monitored the health and development of over 14,000 children from pregnancy.

Mrs. Northstone said, "We have found a small reduction in birth weight in those babies whose mothers smoked cannabis at least once a week before and during their pregnancy."

The researchers found that 5% of mothers had used cannabis at some time before they became pregnant; this use was reduced to less than 3% during pregnancy.

The women who smoked cannabis had similar characteristics to those women that are already known to be most at risk of having babies with low birth weight: younger and first-time mothers and those who use other substances such as alcohol and tobacco.

In the Bristol study, almost 70% of cannabis users also smoked regularly.
The adverse effects of smoking on birth weight are well known, but the association between cannabis use and lower birth weight was still evident after taking smoking and a variety of other factors into account.

Long term follow-up of the children will determine whether there are any adverse effects on the child`s development. Until the results are available, the Bristol scientists recommend that pregnant women should be encouraged to avoid all forms of substance use while they are pregnant.

(Reference: "Maternal use of cannabis and pregnancy outcome". D M Fergusson, L J Horwood, K Northstone and the ALSPAC Study Team, British Journal of Obstetrics and Gynaecology.)

Related websites:

Children of the Nineties

University of Bristol


[Contact: Joanne Fryer ]

08-Jan-2002