Three antiepileptic drugs (carbamazepine, sodium valproate and lamotrigine), are among the most commonly used teratogenic medications in pregnancy, an Australian study shows.

A review of medications used by 145,419 NSW women in 191,588 pregnancies between 2005-2012 found a 2% overall prevalence of exposure to medications in the TGA’s D and X categories for teratogenic medicines.

The most common categories of teratogenic drug used in pregnancy were ‘antipsychotics’ – which comprised mostly anti-epileptic drugs – and antibiotics.

For most drugs the rates of exposure decreased substantially through the course of pregnancy, averaging 4-6% pre-pregnancy to 1.5%  in the first trimester.

But there were only modest reductions in use of antiepileptic drugs  – which come in category D – over the course of  pregnancy, perhaps reflecting the need to balance risks of teratogenic effects with risks of seizures, said the authors of the study published in  the Australia and NZ Journal of Obstetrics and Gynaecology.

For valproate the exposure prevalence remained stable at around 0.22%-0.28%in the pre-pregnancy period, decreasing to 0.14% in the first trimester and to 0.08% in the third trimester.

For carbamazepine the exposure prevalence remained unchanged at around 0.1% in the pre-pregnancy and pregnancy period. Similarly for lamotrigine the exposure prevalence was little changed at around 0.08% in the pre-pregnancy and pregnancy periods.

The study authors noted that “it is not recommended to discontinue valproate in some unresponsive cases of epilepsy.”

“Antiepileptics, which accounted for most of the psychotropic use in our study, may cause fetal malformations and neurodevelopmental disorders in children  exposed in utero. When used for epilepsy, these may be substituted by less teratogenic antiepileptics, for example lamotrigine is safer than valproate in pregnancy,” they wrote.

“However, these safer alternatives may not always be equally effective in controlling epilepsy. The modest reduction in the prevalence of antiepileptic medicine use following conception suggests that continued use was considered necessary.”

The study found that doxycycline was the most widely used drug in pregnancy, with an exposure rate of around 1.3% in the pre-pregnancy period, but decreasing to very low levels during pregnancy.

Use of ‘Category X ‘ teratogenic medications such as isotretinoin, which are strictly contraindicated in pregnancy, was very low, with exposure rates of <0.005% in pregnancy.