Background: Anti-seizure medications (ASMs) are used to treat conditions such as epilepsy and bipolar disorder. Some of these drugs are associated with an increased risk of congenital malformations and adverse developmental outcomes. Objectives: To examine trends in use of ASMs among pregnant women in the Netherlands according to medication safety profile. Methods: Using population-based data from the PHARMO Perinatal Research Network, we assessed trends in use of ASMs among pregnant women in the Netherlands between 1999 and 2019, stratified by medication safety profile. Individual treatment patterns were also assessed. Results: In total, 671,709 pregnancies among 446,169 women were selected, of which 2405 (3.6 per 1000) were ASM-exposed. Over the study period, a significant increase was observed for use of known safest ASMs (0.7-18.0 per 10,000 pregnancies) as well as for those with uncertain risk (5.3-13.4 per 10,000 pregnancies). Use of ASMs with higher risk of congenital malformations decreased significantly (24.8-14.5 per 10,000 pregnancies), except for topiramate (0-6.7 per 10,000 pregnancies). Switches between ASM safety risk categories before and during pregnancy were uncommon; women rather discontinued treatment or switched within the same category. There was no clear change for the proportion using polytherapy during pregnancy (12% overall), however a non-significant trend toward inclusion of known safest ASMs was observed over time (1.9-3.6%). Conclusions: Over the last two decades, there has been an increase in use of known safest ASMs among pregnant women, together with a trend toward newer ASMs with uncertain risk. Only a small proportion of women switched to a safer alternative before or during pregnancy. Altogether, this highlights the need for an expansion of ASM risk knowledge and communication to healthcare providers and women of reproductive age to improve preconception counseling.

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