Safety of medicines taken during pregnancy

Author: Dr Amanda Oakley, Dermatologist, Hamilton, New Zealand, 2013. Updated August 2019.


Introduction

Some medicines and drugs are known to cause fetal harm if taken during pregnancy. Medicines should only be taken if the expected benefits to the mother are greater than the risk to the mother and to the baby. Essential medicines should be taken in the lowest possible dose and for the shortest possible time during pregnancy. The risks of fetal malformation are greatest during the first trimester (the first 12 weeks of gestation). The effect of withdrawal on the newborn baby should be carefully assessed if medicines such as antidepressants are taken during the third trimester (after 28 weeks).

Rarely, problems have also been reported when medicines such as finasteride have been taken by the male partner.

Drug licensing authorities classify medicines according to their risk in pregnancy. Data is limited; many available medicines have not yet been assessed or classified, and unclassified medicines may or may not be safe during pregnancy. Classified drugs may be reclassified as new information becomes available. 

Refer to the individual drug's most up-to-date and approved datasheet when considering prescribing a medication to a pregnant woman.

Australian TGA classification

When prescribing medicines in pregnancy, it is useful for health professionals to access the Australian Government Department of Health Therapeutic Goods Administration (TGA) comprehensive resource, prescribing medicines in pregnancy database.

The definitions of each category are copied below (TGA website accessed 27 August 2019).

Category A

Category A medicines 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 B

Medicines allocated Category B are subcategorised based on animal data, with human data lacking or inadequate.

Category B1: Medicines 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: Medicines 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: Medicines 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.

Medicines in Category B do not imply greater safety than medicines in Category C.

Category C

Category C medicines are medicines which, owing to their pharmacological effects (risk based on the mechanism of action of the medicine), have caused or may be suspected of causing harmful effects on the human fetus or neonate without causing malformations. These effects may be reversible.

Category D

Medicines in Category D are not absolutely contraindicated during pregnancy. However, there is a higher risk of malformations. Category D medicines have caused, are suspected to have caused, or may be expected to cause, an increased incidence of human fetal malformation or irreversible damage. These medicines may also have adverse pharmacological effects.

Category X

Medicines in Category X are absolutely contraindicated in pregnancy with a high risk of permanent damage (ie, these medicines are teratogenic).

Category X medicines 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.

New Zealand approved datasheets are the official source of information for these prescription medicines, including approved uses and risk information. Check the individual New Zealand datasheet on the Medsafe website.

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