Effects of Low Concentrations of Nitrous Oxide on Rat Pregnancy

Pregnant rats were exposed to concentrations of nitrous oxide similar to those present in the operating room during routine occupational exposure for various periods during pregnancy. Those exposed to 15,000 ppm and 1,000 ppm for 24 hours/day had fetal death rates and pregnancies/rat ratios which were significantly different from the controls. Two groups exposed to 1,000 ppm for 8 hours/day also had fetal death rates significantly different from the controls. Exposure for 8 hours/day did not significantly alter the pregnancies/rat ratios. Differences in the fetal death rates between groups exposed from 6 AM to 2 PM and from 2 PM to 10 PM suggest a diurnal variation in the embryotoxic effect of nitrous oxide in the rat.