High cesarean section rate in trisomy 18 births: a potential indication for late prenatal diagnosis.

The frequency of and indications for primary cesarean section delivery of infants with trisomy 18 was evaluated retrospectively by reviewing the obstetric records of the 48 cases of trisomy 18 diagnosed over a 10-year period by three Genetic Centers in Philadelphia. From June, 1969, to June, 1974, four of 20 infants with trisomy 18 were delivered by primary cesarean section (20%). From June, 1974 to June, 1979, the primary cesarean section rate for trisomy 18 rose to 55.6% (15/28). These rates are considerably higher than those for the State of Pennsylvania during the same time intervals (6.10% and 10.00%, respectively). In the latter 5-year interval, 13 of 15 primary cesarean sections were performed for fetal indications, and "fetal distress" was diagnosed in 11 of the 13. The obstetric features of these pregnancies are reviewed. The basis for a clinical suspicion of trisomy 18 during the third trimester and the possible benefit of late-pregnancy prenatal cytogenetic diagnosis in selected cases are discussed.