The benefits and risks of amniocentesis for the assessment of fetal lung maturity.

Amniocentesis for estimation of the lecithin: sphingomyelin (L/S) ratio was performed on 483 patients on 552 occasions. The introduction of this test has been associated with a highly significant (p less than 0-001) decrease of 59 per cent in the incidence of respiratory distress syndrome. The finding of a low L/S ratio (less than 2-0) enabled delivery to be deferred until lung maturity had been reached in 43 (10-3 per cent) of the 419 patients who had successful amniocentesis. Fetal death occurred after amniocentesis in two patients (0-41 per cent). One fetus died after haemorrhage occurred behind an anterior placenta and the other died of exsanguination. Failed amniocentesis occurred in 64 patients (13-2 per cent), and was more common when the placenta was anterior or was not located before the procedure and when fetal growth was retarded. Fetal distress in labour occurred more commonly after failed amniocentesis. Spontaneous labour followed amniocentesis in 47 patients (9-7 per cent) and was significantly more prone to occur after 38 weeks gestation. Rhesus isoimmunization did not occur in any of the rhesus-negative patients who delivered rhesus-positive babies and who were screened six or more months after amniocentesis, although anti-D immunoglobulin was not given routinely after amniocentesis. Suggestions are made as to how the success rate of this valuable procedure can be improved and how some of the serious fetal and maternal sequelae can be avoided.