Medicines in pregnancy

An Australian categorisation of risk of drug use in pregnancy*

The categories defined below are limited to those referred to in these guidelines. The categorisation applies only to recommended therapeutic doses in women in the reproductive age group. In situations such as overdose, occupational exposure and others when the recommended dose is exceeded, it cannot be assumed that the classifications assigned to individual medicines are valid.

Category A Drugs which have been taken by a large number of pregnant women and women of childbearing 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 childbearing 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 childbearing 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 childbearing 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. Accompanying 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. Accompanying 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.

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.

* Based on: Medicines in Pregnancy Working Party of the Australian Drug Evaluation Committee, 1999, Prescribing medicines in pregnancy. An Australian categorisation of risk of drug use in pregnancy, 4th edn, Therapeutic Goods Administration, Canberra (accessed 21.06.10)