There are particular risks involved in drug use during pregnancy and standard advice to all pregnant women is to avoid if at all possible the use of any mood changing drug during pregnancy unless administered under medical supervision.

Crossing the placenta.

During pregnancy the placenta acts as a filter between the mother's and baby's bloodstream, allowing tiny molecules to pass from mother to baby whilst preventing larger particles from crossing. As drug molecules are relatively small they can pass easily across the placenta. Because of this most drugs being taken by the mother will find their way into the bloodstream of the foetus. This can result in children born to women dependent on heroin, for example, to experience withdrawal symptoms at birth.

Three trimesters.

Pregnancy is divided into three, three-month-long stages called trimesters. There are risk issues for each trimester.

The first trimester of pregnancy is the most critical period as some drugs can affect the development of foetal organs and, in severe cases have caused miscarriage.

During the second trimester - months four, five and six - some drugs may retard the baby's growth, resulting in a low birth weight. Low birth weight babies suffer much higher rates of developmental problems, childhood illnesses etc.

In the final three months, some drugs can affect labour causing it to be premature, delayed or prolonged.

What should pregant drug users do?

As the first trimester is such a crucial period it is vital that women drug users seek ante-natal care as soon as they find out they are pregnant. Unfortunately, the stigma surrounding women's drug use is such that many are reluctant to seek help due to their fear of having their child removed from them soon after the birth.

In fact this happens only rarely as both the physical and emotional welfare of mother and child are paramount during this period and are best served in the vast majority of cases by staying together. Pregnant women drug users need understanding and support from all the professionals around them if they are to take full advantage of the services available to improve their health and that of their babies.

Breast feeding.

Some drugs can also pass from mother to baby after the birth if the child is breast fed. As the milk producing glands in the breast are surrounded by fine blood vessels it is possible for tiny amounts of a drug present in the mothers blood to be passed on to the baby through the milk. In most cases the amount of the drug would be so small that it would have little effect on the newborn, but this may not be the case for drugs which are soluble in fat, such as cannabis.