A normative study of obstetric complications associated with fetal trisomy 18.

Our objective was to determine whether the cesarean section rate and amniotic fluid lecithin-sphingomyelin ratio (L/S ratio) associated with fetal trisomy 18 are different from those associated with euploid pregnancies. Forty-nine trisomy 18 pregnancies were identified and their records were reviewed. Of the 22 live-born infants, 15 (68%) were delivered by cesarean section. The overall cesarean section rate for the institution ranged from 19.1% to 22.6%. In five patients with gestational ages between 35 and 38 weeks who had amniocentesis as part of the evaluation of intrauterine growth retardation, the L/S ratios were < or = 1.8. These data confirm that undiagnosed trisomy 18 pregnancies are associated with an increased cesarean section rate. Further, trisomy 18 fetuses appear to have delayed maturation of the L/S ratio. These results reinforce the importance of a karyotypic evaluation of selected pregnancies complicated by intrauterine growth retardation, even in the third trimester, and suggest that the prenatal diagnosis of trisomy 18 is of obstetric importance.