Objective To investigate the impact of epilepsy and antiepileptic drugs on length of gestation and anthropometric measures of the newborn.

Design Cohort study based on questionnaires mailed to all pregnant women who attended for prenatal care at our department from August 1989 to January 1997.

Setting Department of Obstetrics and Gynaecology at Aarhus University Hospital, Denmark.

Participants One hundred and ninety-three singleton pregnancies in women with epilepsy were compared with 24,094 singleton pregnancies in women without epilepsy.

Main outcome measures Preterm delivery, small for gestational age, mean gestational age, gestational age-adjusted birthweight, head circumference, and body length.

Results Children of women with epilepsy who smoked had lower gestational age and were at increased risk of preterm delivery (OR 3.4; 95% CI 1.8–6.5), compared with children born by nonepileptic women who smoked. Birthweight adjusted for gestational age was reduced by 102 g (95% CI 40–164) in women with epilepsy, and the risk of delivering a child who was small for gestational age was increased (adjusted OR 1.9, 95% CI 1.3–2.7), compared with women without epilepsy. Newborn babies of women with epilepsy treated by drugs had a reduced adjusted birthweight (208 g, 95% CI 116–300), head circumference (0.4 cm, 95% CI, and body length (0.5 cm, 95% CI 0.1–1.0), compared with the newborn infants of women without epilepsy.

Conclusions Women with epilepsy who smoked were at increased risk of preterm delivery compared with healthy smokers. Children of women with drug treated epilepsy had lower birthweight, length, and head circumference than children of women without epilepsy.