Labor decreases the lung water content of newborn rabbits.

To test the prevailing concept that drainage of fetal lung liquid begins after birth, we measured extravascular lung water content of 47 fetal rabbits born at term gestation, with or without prior labor. Rabbits born after labor, either vaginally or operatively, had less water in their lungs than those delivered by cesarean section without preceding labor; there was no difference in lung water content between rabbits born vaginally or operatively after labor. These results suggest that reduction in the volume of fetal lung liquid in rabbits normally begins before birth and depends on the experience of labor, not the mode of delivery.