According to authors Sonia Hernandez-Diaz et al. in the study “Topiramate use early in pregnancy and the risk of oral clefts” :
The increased risk of oral clefts associated with use of Topiramate early in pregnancy was more pronounced in women with epilepsy who used higher doses.
[The study’s objective was] to assess the relative risk of oral clefts associated with maternal use of high and low doses of Topiramate during the first trimester for epilepsy and nonepilepsy indications.
Approximately one out of every 1,000 infants are born with an oral cleft, but among infants exposed to low doses of Topiramate (median 100-mg daily dose) in the first trimester, that risk was 2.1 out of every 1,000 live births. Among women taking higher dose Topiramate (median 200-mg daily dose), the risk was much higher — 12.3 for every 1,000 live births.
Women with epilepsy on Topiramate have the highest relative risk of giving birth to a baby with cleft lip or cleft palate, likely due to the higher doses of Topiramate when used for controlling seizures.