Nitrous oxide in early human pregnancy.

An analysis of the outcome of 375 cases (383 fetuses) of cervical cerclage and 58 other operations (59 fetuses) conducted under general anaesthesia, which included the administration of nitrous oxide, failed to reveal a single instance of which nitrous oxide could have been clearly indicted as a cause of fetal abnormality The incidence of inevitable abortion and of low birth weight babies in the series of cervical cerclage conducted under general anaesthesia was identical to that in a series conducted under regional analgesia (115 fetuses). This represents the first of a two-part test of the proposition that nitrous oxide should not be administered to women in the first or second trimester. Our interim conclusion is that the proposition is unacceptable.