This study investigates the impact of generalized tonic-clonic seizures (GTCS) and antiepileptic drugs (AED) during pregnancy on gestational age (GA) and anthropometric data of newborns. One hundred twenty-nine singleton pregnancies resulting in live births from September 1999 to October 2010 in 106 women with epilepsy on AED therapy, recorded within the framework of the EURAP (International Registry of Antiepileptic Drugs and Pregnancy) program at the Department of Neurology, Medical University Innsbruck, Austria, were studied. Occurrence of ≥ 1 GTCS during pregnancy was associated with a shorter GA [median (range) 37.5 [35.1-41.6] vs. 39.7 [29.1-46.3] weeks; p ≤ 0.001], an overall five times higher preterm risk (p = 0.042) and a reduced birth weight in boys (2,900 [2,050-3,870] vs. 3,205 [1,575-4,355] g; p = 0.040). In primipara, when compared to multipara, GTCS ≥ 1 significantly reduced the GA (37.9 [35.1-41.6] vs. 39.7 [29.4-44.9] weeks; p = 0.020) and raised the incidence of low birth weight (LBW) (p = 0.022) in neonates. Antiepileptic drug polytherapy significantly increased the risk for small-for-gestational-age regarding weight (SGA(W); p = 0.035) and regarding weight and/or length (SGA(W/L); p = 0.046) when compared to monotherapy. GTCS during pregnancy was associated with diverse negative effects comprising shorter GA, an increased incidence of prematurity and LBW in primiparous women. Furthermore, AED polytherapy was correlated with an enhanced risk for SGA delivery. Re-evaluating the need for drug therapy (in particular polytherapy), maintaining seizure control for a given period before pregnancy and counseling about the importance of preventing GTCS might improve pregnancy outcome in women with epilepsy.