Babies with pure esophageal or duodenal atresia weight less than normal babies at birth. Whether this is due to the obstruction to fetal swallowing or some other cause is not known. To determine how intrauterine interruption of swallowing affects fetal growth, we developed a model of esophageal atresia in the fetal rabbit. Twenty-five time-mated rabbits at 24 days gestation were anesthetized with halothane and ketamine. The uterus was exposed through a midline abdominal incision. The head and neck of the fetus in the distal end of one horn were isolated through a 2-cm hysterotomy. Biparietal diameter (BPD) was measured and the esophagus was isolated and ligated through a midline cervical incision. The fetus in the distal end of the opposite horn underwent sham operation. Four days later, cesarean section was done. The newborn rabbits were weighed, and crown/rump length and BPD were measured. Ligation of the esophagus was confirmed by re-exploration of the neck. Three does died under anesthesia and two aborted. From the remaining 20, 156 fetuses were recovered, of which 135 were alive. One set of operated fetuses was dead, leaving 19 pairs for analysis. There was a statistically significant reduction in weight gain (31.7 +/- 1.3 g to 29.1 +/- 0.9 g, P less than 0.05) following interruption of the esophagus but linear growth was unchanged. Obstruction to normal fetal swallowing may account for the low birth weight with normal head circumference reported in babies with esophageal and duodenal atresia.