The medic's guide to prescribing: Prescribing in pregnancy

When a baby is born with a congenital defect, parents and professionals look for a cause. As most women use over the counter or prescription drugs at some stage of their pregnancy, drugs are often indicted as the probable culprit-guilt by association.

Studies that look at causality are less impressive-teratogens (drugs or chemicals that cause abnormal development in cells and tissues) are thought to contribute to a minority (2.5%) of all congenital malformations.1 Nevertheless the thalidomide tragedy of the 1960s, when thousands of babies were born with short or absent limbs after their mothers had taken thalidomide as a treatment for morning sickness, still colours the perception of patients and doctors.

Prescribing practice is shaped by anecdotal reports, retrospective series, and extrapolations from animal studies, especially as randomised placebo controlled trials in pregnancy are exceedingly rare. Prescribing in this emotionally charged setting without the backup of strong scientific evidence is a daunting challenge. But women will continue to have babies and perfect health cannot be guaranteed for everyone during their nine months of pregnancy, so it is advisable to have an approach to prescribing for pregnant women. Here we use a fictitious case study to highlight some important points to consider.

Ms P, a 26 year old woman, was admitted to hospital after a generalised seizure. She is known to have epilepsy and had been seizure-free for the past five years while taking lamotrigine. On admission her examination was unremarkable, but she had a positive pregnancy test. At that time Mrs P was nine weeks pregnant, and on closer questioning admitted to having discontinued her drugs three weeks earlier because of concerns of harming her …