Triply discordant triplets: probability, management options, and risks.

The spontaneous occurrence of triplets is rare. With increased utilization of "assisted reproductive technologies," multifetal gestations have become more common. The empiric fetal risk for major malformation is approximately 3%. In a triplet pregnancy each fetus independently carries this risk so that the probability of having at least one malformed fetus is approximately 9%. It is much less likely to have 2 or 3 simultaneously but discordantly malformed fetuses in a multizygotic triplet gestation (.09% and .0027% risk, respectively). We report on the first case, to our knowledge, of an ovulation-stimulated triplet pregnancy complicated by 3-way discordance for major malformations diagnosed in the late second trimester by ultrasound. Fetus A was affected by congenital diaphragmatic hernia and trisomy 21; fetus B had encephalocele, a midline facial defect, and a cleft palate; and fetus C had evidence of unilateral claw hand but an otherwise normal fetal survey. At 19 weeks of gestation, fetus A was found to have spontaneously died, and a selective termination of triplet B was performed. We conclude: (1) the finding of a single major malformation in one fetus should lead to extensive search for malformations in all members of the pregnancy, and (2) the simultaneous occurrence of major malformations in more than one member of a multifetal gestation is a circumstance under which multiple selective termination deserves consideration. In this article we discuss important issues and caveats in the performance of selective termination for abnormal members of multifetal gestations.