Caution is needed in all women of childbearing age

Doctors, patients, and the pharmaceutical industry are all cautious about the use of drugs during pregnancy.1 Few applications for product licences for new drugs include use in pregnancy, and the British National Formulary warns that all drugs should be avoided if possible during the first trimester. Inflexible application of this guideline may lead to pregnant women being denied effective drug treatments. By contrast, lack of awareness of the risks may allow potentially teratogenic drugs to be prescribed to pregnant women and, much more commonly, to women of childbearing age who may become pregnant.

Drugs can cause fetal death or damage at any stage of pregnancy. Anticancer drugs, for example, inhibit cell replication and so may cause the death of the embryo during blastocyst formation (0-16 days). Later in pregnancy (second and third trimester), drugs such as β blockers may cause general retardation of growth, while others may affect maturation of specific organ systems—for example, angiotensin converting enzyme inhibitors cause abnormalities of renal function and skull development.2 …