Relationship between ossification and body weight of the CD-1 mouse fetus exposed in utero to anticonvulsant drugs.

The anticonvulsant drugs carbamazepine, Na valproate, and phenytoin have been suspected as a cause of human congenital defects. The malformations produced may include cleft lip and/or palate, heart defects, skeletal defects, and low body weights. Since the toxic effects of these anticonvulsant drugs manifest themselves in terms of fetal growth retardation, evaluation of the state of ossification attained in the fetus is important. In the present study, pregnant CD-1 mice received on gestational days 8-16 an oral dose of 375, 563, 938 mg/kg of carbamazepine; or 225, 338, 563 mg/kg of Na valproate; or 50, 75, 125 mg/kg of phenytoin. These groups were compared to two control groups. On day 17, the dams were killed by cervical dislocation and one-third of the live fetuses were weighed and fixed for skeletal examination. Photographs were taken of the fore- and hindlimb skeletons. From these photographs, the length and width measurement of ossified regions of the humerus and femur were determined using a Zeiss Video-Plan Morphometrics Computer. Of the three anticonvulsant drugs studied, the greatest correlation between reduced fetal weights and retarded ossification of the long bones was phenytoin at the 125 mg/kg dosage. Our results also showed that long bone ossification, when compared to the fetal weight, indicated that 59-66% of variability in weight is predictable by bone measurements.