Selective Fetal Reduction for an Anomaly in a Twin Gestation

A 32-year-old Gravida 4 Para 1-0-2-1 woman was seen by Maternal Fetal Medicine at 12 weeks 3 days’ gestation for dichorionic diamniotic twins. Her history was significant for 2 first-trimester miscarriages requiring dilation and evacuation. At the time of the consultation, the early first-trimester ultrasound for Twin B was reassuring. The ultrasound for Twin A demonstrated a cystic hygroma and omphalocele (Figure 1).The pregnant patient and her partner were counseled about the findings and prognosis of Twin A. Given the anomalies in Twin A and the potential of preterm delivery and complications of an ongoing twin pregnancy for Twin B, the couple opted for selective fetal reduction (SFR). An ultrasound-guided SFR was performed with a 22-gauge needle and intracardiac injection of potassium chloride. At the time of the procedure, chorionic villus sampling was performed for genetic testing for Twin A.The pregnant patient returned the following week at 13 weeks 3 days’ gestation, and normal fetal cardiac activity was noted for Twin B with a known demised Twin A. The chromosomal analysis from chorionic villus sampling of Twin A resulted in monosomy X. The patient declined diagnostic testing for Twin B.The remainder of the pregnancy was notable for the development of gestational hypertension, and induction of labor was recommended at 37 weeks’ gestation. The pregnant patient had a vaginal delivery of a liveborn male infant weighing 3200 g with an Apgar score of 8 at 1 and 5 minutes. The neonate was admitted to the neonatal intensive care unit for cyanosis requiring nasal cannula oxygen, which was weaned over the next few days; the infant was subsequently discharged home 5 days after birth. A microarray analysis from the cord blood of the neonate resulted as normal.Twins can be classified by either zygosity, which refers to the genetics shared between the 2 fetuses, or chorionicity, which refers to the placental structure between the 2 fetuses. In dizygotic fertilization, 2 oocytes are fertilized separately by different sperm, which go on to form a dichorionic-diamniotic pregnancy. This dual fertilization accounts for 70% of twin pregnancies.1 Dizygotic twins from spontaneous conceptions share approximately 50% of genetic material, similar to non-twin siblings.1Thirty percent of twin pregnancies are monozygotic, in which a single oocyte is fertilized by a single sperm, and the twins have a shared genotype.1 The timing of division of the zygote into 2 separate embryos determines the chorionicity. As seen in Figure 2, of all monozygotic twin pregnancies, 20% to 30% will be dichorionic-diamniotic following cleavage of the zygote within 4 days of fertilization. A total 70% to 75% of monozygotic twins are monochorionic, diamniotic with cleavage between days 4 and 8. A total 1% to 2% of monozygotic twins are monochorionic, monoamniotic with cleavage between days 9 and 12.2,3Establishing chorionicity early in pregnancy is key due to the increased perinatal morbidity and mortality of monochorionic twins because of shared placental vasculature. Dichorionicity is established with an early ultrasound that shows 2 gestational sacs with a “lambda sign” (Figure 3), which is a thickened projection of placental tissue between the twins’ membranes. In contrast, monochorionic twin gestations have a “T sign” on ultrasound, with a thin intertwin membrane perpendicular to the placenta (Figure 4).2Twin pregnancies are associated with increased rates of pregnancy morbidity and mortality. The rate of stillbirth for twins is 12 per 1000 births compared to 5 per 1000 births in singleton pregnancies.4 In the United States, more than 5 of every 10 twin pregnancies are delivered prematurely compared to 1 in every 10 singleton pregnancies.5 The rate of preterm delivery can result from spontaneous labor or secondary to an iatrogenic delivery for indications in the pregnant patient or fetus.4 Neonatal morbidity is correlated with the gestational age at time of delivery. Twins born prior to 32 weeks’ gestation have a 2-fold increased risk of high-grade intraventricular hemorrhage and a 4-fold increased risk of cerebral palsy compared to singletons.6,7 Neonates born to a twin gestation are at 5 to 7 times increased risk of neonatal mortality compared to singleton pregnancies.4,5 In particular, monochorionic twin gestations are at higher risk of complications compared to dichorionic twins. Monochorionic twin gestations have more than twice the risk of perinatal mortality due to the increased risk of anomalies and vascular complications from the shared placenta.2Of twin pregnancies, 1% to 2% will have discordant fetal anomalies in which only 1 fetus has an anomaly.4 The risk of a fetal anomaly is dependent on the type of twins; dizygotic twins have a similar rate per fetus of fetal abnormalities as singletons (2%–3%), and thus the chance that one twin is affected is greater than that for a singleton pregnancy.8,9 In contrast, monozygotic twins have a 2- to 3-fold increased risk of fetal anomaly, but in less than 20% of cases will both twins be affected by the same anomaly.4 Discordance of fetal anomalies in monozygotic twins can be attributed to the unequal division of genetic material at the blastomere level into the 2 embryos.10In addition to discordant structural abnormalities and aneuploidy in twins, monochorionic twins are at risk of complications due to the shared circulatory connections between the 2 fetuses, resulting in a bidirectional flow of blood.11 As such, there can be an imbalance in blood flow, leading to unique complications specific to monochorionic pregnancies such as twin-to-twin transfusion syndrome, twin anemia polycythemia sequence, and twin reversed arterial perfusion. Due to placental anastomoses of monochorioic pregnancies, the death of one fetus can result in neurological damage or the demise of the surviving twin in 12% to 26% of cases.12 Risks and benefits from SFR are outlined in Table 1.SFR refers to the preferential termination of one fetus in multiple gestation, typically because of a structural or genetic abnormality. This procedure may also be done in a fetus without anomalies in high-order gestation to decrease the risk for previable and early preterm delivery. Due to varying legal restrictions on abortion across different states, options for SFR are limited in many situations. In twin pregnancies, the presence of an anomalous twin is associated with an increased rate of preterm delivery, low birth weight, and mortality of the co-twin without anomalies.13 Therefore, selective reduction of the abnormal twin may improve the outcomes of the surviving twin by reducing the likelihood of twin complications.The chorionicity of the twin gestation affects how an SFR can be performed. In dichorionic pregnancies, SFR is performed using potassium chloride or lignocaine, which is injected intracardiac or into the umbilical cord of one twin.4 Due to the shared vascular connections, this SFR method is contraindicated in monochorionic pregnancies.4 SFR in monochorionic pregnancies alternatively uses several techniques, with the goal of immediately stopping the exchange of blood between the twins, including coagulation of the umbilical cord, interstitial laser coagulation, and radiofrequency ablation.14The rate of complications from SFR in any type of twins is correlated with the gestational age in which the procedure is performed. SFR performed in the second trimester has higher risk of miscarriage (7%) and preterm birth (14%) compared to SFR in the first trimester.4 Overall, the loss of the co-twin is 2.5% after the procedure with the greatest risk of demise occurring within 2 weeks after the procedure.15,16 The most frequent complication of SFR is a premature pre-labor rupture of membranes prior to 32 weeks’ gestation, which occurs in 20% of cases.4The overall survival rate of the healthy co-twin is 80% after SFR.4 In one systematic review, neonatal morbidity (respiratory distress syndrome, stage 2 or greater necrotizing enterocolitis, neonatal sepsis, severe cerebral injury, renal failure, or patent ductus arteriosus requiring treatment) was 14%, with a neonatal death rate of 4%.14 In one study, overall adverse events including perinatal mortality occurred in 36.6% of surviving co-twins, with 6.8% having neurodevelopmental impairment.17 These rates of morbidity and mortality are associated with earlier gestational age at the time of delivery. It should be noted that SFR reduces the risk of premature delivery prior to 37 weeks’ gestation.16,17SummaryThis case highlights the complexity of twin gestations complicated by discordant anomalies. SFR in the setting of discordant anomalies in twin pregnancies presents a viable option for optimizing perinatal outcomes. The procedure offers potential benefits, including lowering the risk of preterm birth, pregnancy complications, and long-term neonatal morbidity. In this case, an SFR for discordant anomalies in a dichorionic twin gestation resulted in a healthy singleton at term.American Board of Pediatrics Neonatal-Perinatal Content SpecificationKnow maternal medical disorders and medications affecting the fetus and newborn infantUnderstand the complexities that come with multiple gestation cases