For patients with epilepsy, anti-epileptic medication is generally the first line of treatment, but treating pregnant women with epilepsy can be a challenge. Standard anti-epileptic medications have caused developmental abnormalities, so much effort has been put into developing antiepileptic medications with minimal teratogenic effects. In this experimental study, the new-generation anti-epileptic medication levetiracetam and the standard anti-epileptic medication valproic acid were compared in terms of teratogenicity by studying embryonic development in 360 fertile White-Leghorn chicken eggs (conception day 0). We found that levetiracetam may cause severe developmental abnormalities, and is likely not safe for use in pregnant women. As expected, valproic acid caused more frequent developmental abnormalities than levetiracetam, and the risk increased still further when both drugs were administered in combination. Levetiracetam should be used cautiously in pregnant women with epilepsy. (C) 2010 Elsevier Ltd. All rights reserved.