Reduction of a selected fetus or fetuses in a multichorionic multifetal gestation may be chosen as a therapeutic intervention to enhance survival of the remaining fetuses (American College of Obstetricians and Gynecologists, 20 17b). One metaanalysis of nonrandomized prospective studies indicates that pregnancy reduction to twins compared with expectant management is associated with lower rates of maternal complications, preterm birth, and neonatal death (Dodd, 2004, 2012).
Pregnancy reduction can be performed transcervically, transvaginally, or transabdominally, but the transabdominal route is usually easiest. Transabdominal fetal reductions are typically performed between 10 and 13 weeks' gestation. This gestational age is chosen because most spontaneous abortions have already occurred, the remaining fetuses are large enough to be evaluated sonographically, the amount of devitalized fetal tissue remaining after the procedure is small, and the risk of aborting the entire pregnancy as a result of the procedure is low. The smallest fetuses and any anomalous fetuses are cho sen for reduction. Potassium chloride is then injected under sonographic guidance into the heart or thorax of each selected fetus. Care is used to avoid entry or traverse the sacs of fetuses selected for retention.
pregnancies from 1995 to 1998. he pregnancy loss rate var ied from a low of 4.5 percent for triplets that were reduced to twins. The loss rate rose with each addition to the starting num ber of fetuses and peaked at 15 percent for six or more fetuses.
Operator skill and experience are believed responsible for the low and declining rates of pregnancy loss.
With the identification of multiple fetuses discordant for struc tural or genetic abnormalities, three options are available: abor tion of all fetuses, selective termination of the abnormal fetus, or pregnancy continuation. Because anomalies are typically not discovered until the second trimester, selective termination is greater risk. This procedure is therefore usually not performed unless the anomaly is severe but not lethal. In some cases, ter mination is considered because the abnormal fetus may jeopar dize the normal one.
Prerequisites to selective termination include a precise diagnosis for the anomalous fetus and absolute certainty of fetal location. Unless a special procedure such as umbilical cord interruption is used, selective termination should be performed only in multichorionic multifetal gestations to avoid damaging the surviving fetuses (Lewi, 2006). Roman and coworkers (2010) compared 40 cases of bipolar umbilical cord coagulation with 20 cases of radiofrequency ablation for treatment of complicated monochorionic multifetal gestations at midpregnancy. hey found similar survival rates of 87 and 88 percent, and a median gestational age > 36 weeks at delivery in both. Prefumo and colleagues (2013) reported their preliminary experience with microwave ablation of the umbilical cord for selective termination in two monochorionic twin pregnancies. One pregnancy aborted within 7 days, and the other resulted in a term singleton delivered at 39 weeks' gestation.
Evans and coworkers (1999) have provided the most comprehensive results to date on second-trimester selective termination for fetal abnormalities. A total of 402 cases were analyzed from eight centers worldwide. Included were 345 twin, 39 triplet, and 18 quadruplet pregnancies. Selective termination using potassium chloride resulted in delivery of a viable neonate or neonates in more than 90 percent of cases, with a mean age of 35.7 weeks at delivery. The entire pregnancy was lost in 7 percent of pregnancies reduced to singletons and in 13 percent of those reduced to twins. The gestational age at the time of the procedure did not appear to afect the pregnancy loss rate.