Prescribing for pregnant women

Be careful when prescribing for pregnant women and women of child-bearing age, as drugs may cause harm to a fetus at any time during pregnancy. Teratogenic drugs taken during the first trimester may cause congenital malformations. In the second and third trimesters, fetal growth and functional development may be affected by drugs; some drugs taken during this period may affect the fetus, while some drugs given close to term may have adverse effects on labour or on the neonate.

Generally, our advice is based on human data and clinical experience. Animal studies are not used as sole sources of information upon which advice is based, as their interpretation with respect to human risk is not clear. Advice provided may not mirror the Approved Product Information. Absence of information in AMH does not imply safety.

Australian Drug Evaluation Committee (ADEC) categories of safety, from the booklet Prescribing Medicines in Pregnancy, are included where they exist. As this booklet indicates, the categorisation and information provided is aimed at assisting the planning of medical management of patients who are pregnant or intend to become pregnant.

Practice points

• prescribe drugs during pregnancy only if the expected benefit to the mother is thought to be greater than the risk to the fetus
• counsel pregnant women to avoid exposure to all unnecessary drugs and chemicals
• few drugs have been shown conclusively to be teratogenic in humans, but no drug is safe beyond all doubt in early pregnancy
• some drugs have been used widely during pregnancy and appear to be safe; in general, prescribe these rather than new or untried drugs
• detailed advice is available from pregnancy drug information centres

ADEC pregnancy categories

Category A

Drugs which have been taken by a large number of pregnant women and women of child-bearing age, without any proven increase in the frequency of malformations or other direct or indirect harmful effects on the fetus having been observed.

Category B1

Drugs which have been taken by only a limited number of pregnant women and women of child-bearing age, without an increase in the frequency of malformation or other direct or indirect harmful effects on the human fetus having been observed. Studies in animals have not shown evidence of an increased occurrence of fetal damage.

Category B2

Drugs which have been taken by only a limited number of pregnant women and women of child-bearing age, without an increase in the frequency of malformation or other direct or indirect harmful effects on the human fetus having been observed. Studies in animals are inadequate or may be lacking, but available data show no evidence of an increased occurrence of fetal damage.

Category B3

Drugs which have been taken by only a limited number of pregnant women and women of child-bearing age, without an increase in the frequency of malformation or other direct or indirect harmful effects on the human fetus having been observed. Studies in animals have shown evidence of an increased occurrence of fetal damage, the significance of which is considered uncertain in humans.

Category C

Drugs which, owing to their pharmacological effects, have caused or may be suspected of causing, harmful effects on the human fetus or neonate without causing malformations. These effects may be reversible. Specialised texts should be consulted for further details.

Category D

Drugs which have caused, are suspected to have caused or may be expected to cause, an increased incidence of human fetal malformations or irreversible damage. These drugs may also have adverse pharmacological effects. Specialised texts should be consulted for further details.

Category X

Drugs which have such a high risk of causing permanent damage to the fetus that they should not be used in pregnancy or when there is a possibility of pregnancy.

Additional information about the ADEC categories

For drugs in the B1, B2 and B3 categories, human data are lacking or inadequate and subcategorisation is therefore based on available animal data. The allocation of a B category does not imply greater safety than the C category. Drugs in category D are not absolutely contraindicated in pregnancy (eg anticonvulsants). Moreover, in some cases the D category has been assigned on the basis of suspicion.