Nitrous oxide and the fetus. A review and the results of a retrospective study of 175 cases of anaesthesia for insertion of Shirodkar suture.

The outcome of 175 pregnancies during which nitrous oxide was administered has been evaluated. All anaesthetics were of short duration (20-30 min) and 97% were administered during the second trimester. No adverse effects were identified. The mechanism of potential toxicity and the implications of the use of nitrous oxide during the first and second trimesters of pregnancy are discussed.