Other investigations have found similar trends (Danon, 2013;
Hillman, 2011; Mahony, 2011).
Other factors that afect the prognosis for the surviving twin include gestational age at the time of the demise and duration between the demise and delivery of the surviving twin. With a vanishing twin, the risk of death after the irst trimester is not increased for the survivor. However, when a fetus dies in the second trimester or later, the efect ofgestational age at the time ofdeath and the mortality risk to the cotwin are less clear. In an analysis by Hillman and colleagues (2011), cotwin demise rates were unafected regardless of whether the irst death occurred at 13 to 27 weeks' gestation or at 28 to 34 weeks. In cases with the death ofone twin after the irst trimester, however, the odds of spontaneous and iatrogenic preterm delivery of the remain ing living twin were increased (Hillman, 2011). Preterm birth gestation. Ifthe fetus died after 34 weeks, preterm delivery rates were similar.
The neurological prognosis for a surviving cotwin depends almost exclusively on chorionicity. In their comprehensive review, Ong and coworkers (2006) found an 18-percent rate of neurological abnormality in twins with monochorionic placentation compared with only 1 percent in those with dichorionic placentation. In another review, in twin pregnancies complicated by a single fetal demise before 34 weeks, a ivefold higher risk ofneurodevelopmental morbidity was identiied in monochorionic twins compared with dichorionic twins. If the one fetus died after 34 weeks, the likelihood ofneurological deicits was essentially the same between monochorionic and dichorionic twin pregnancies (Hillman, 201r1).
Later in gestation, the death ofone ofmultiple fetuses could theoretically trigger coagulation defects in the mother. Only a few cases of maternal coagulopathy after a single fetal death in a twin pregnancy have been reported. This is probably because the surviving twin is usually delivered within a few weeks ofthe demise (Eddib, 2006). That said, we have observed transient, spontaneously corrected consumptive coagulopathy in multifetal gestations in which one fetus died and was retained in utero along with its surviving twin. he plasma ibrinogen concentration initially decreased but then increased spontaneously, and the level of serum ibrinogen-ibrin degradation products increased initially but then returned to normal levels. At delivery, the portions of the placenta that supplied the living fetus appeared normal. In contrast, the part that had once provided for the dead fetus was the site of massive ibrin deposition.
Decisions should be based on gestational age, the cause of death, and the risk to the surviving fetus. First-trimester losses require no additional surveillance for this speciic indication. If the loss occurs after the irst trimester, the risk ofdeath or damage to the survivor is largely limited to monochorionic twin gestations. Morbidity in the monochorionic twin survivor is almost always due to vascular anastomoses, which often cause the demise of one twin followed by sudden hypotension in the other (p. 878). For this reason, if one fetus of a monochorionic twin gestation dies ater the first trimester but before viability, pregnancy termination can be considered (Blickstein, 2013). Occasionally, death of one but not all fetuses results from a maternal complication such as diabetic ketoacidosis or severe preeclampsia with abruption. Pregnancy management is based on the diagnosis and the status of both the mother and surviving fetus. If the death of one dichorionic twin is due to a discordant congenital anomaly in the irst trimester, it should not afect the surviving twin.