Outcomes in twin pregnancies reduced to singleton pregnancies compared with ongoing twin pregnancies Simi Gupta, MD; Nathan S. Fox, MD; Jessica Feinberg, BS; Chad K. Klauser, MD; Andrei Rebarber, MD OBJECTIVE: Multifetal pregnancy reduction has been shown to improve outcomes in triplet and higher-order multiple pregnancies. The data for fetal reduction of twin pregnancies are limited. The purpose of this study was to compare adverse pregnancy outcomes in ongoing twin pregnancies compared with twin pregnancies reduced to singletons. STUDY DESIGN: This was a retrospective cohort study comparing dichorionic diamniotic twin pregnancies with dichorionic diamniotic twin pregnancies reduced to singleton gestations between 11 and 24 weeks’ gestation in a single maternal-fetal medicine practice over a 9 year period. Adverse pregnancy outcomes after 24 weeks were compared, with a value of P < .05 used for significance. RESULTS: Five hundred one ongoing twin pregnancies and 63 twin pregnancies reduced to singletons were included. Patients with reductions to singletons had a significantly lower risk of preterm delivery before 37 weeks’ gestation (10% vs 43%; P < .001) but no difference in the risk of preterm delivery before 34 weeks’ or 28 weeks’ gestation. Patients with reductions to singletons also had a lower risk of infant birthweight less than the 10% (23% vs 49%; P < .001) but no difference in the risk of infant birthweight less than the 5%. There was no difference in the risk of fetal demise after 24 weeks’ gestation. CONCLUSION: Fetal reduction of twin pregnancies decreases the risk of late preterm birth and birthweight less than the 10% but not the risks of more severe complications such as early preterm birth or birthweight less than the 5%. Key words: multifetal pregnancy reduction, selective reduction, twin pregnancy Cite this article as: Gupta S, Fox NS, Feinberg J, et al. Outcomes in twin pregnancies reduced to singleton pregnancies compared with ongoing twin pregnancies. Am J Obstet Gynecol 2015;213:580.e1-5. M ultifetal pregnancy reduction was developed to reduce higher- order multiple pregnancies to singleton or twin pregnancies in the attempt to improve several pregnancy outcomes but most importantly preterm birth. 1-3 With improvements in infertility treatments, the number of triplet and higher-order pregnancies has dropped 9% from 2011 to 2012 and more than a third since its peak in 1998. 4 Twin births, how- ever, have remained stable over the last several years. 4 The benefit of fetal red- uction from twins to singletons remains controversial. Compared with singleton pregnan- cies, twin pregnancies are associated with an increase in fetal, infant, and maternal morbidity. Infant morbidity includes an increased risk of intrauter- ine growth restriction and preterm de- livery with the associated complications of prematurity. Maternal morbidity in- cludes an increased risk of gestational diabetes, hypertension, hemorrhage, and cesarean delivery. 5 Multifetal reduction from twin preg- nancies to singleton pregnancies may be performed for a number of reasons including an increased risk for infant or maternal complications based on maternal or obstetric history, to decrease the known complications of twin pr- egnancies, or for social reasons. Sele- ctive reduction may also be performed because of a genetic or congenital an- omaly in one of the fetuses. Fetal reduction to singletons in 52 twins by a single operator and 82 twins by multiple operators was shown to decrease the risk of preterm delivery and low birthweight when compared with national databases of ongoing twin pregnancies. 6,7 However, in one small retrospective study comparing 35 on- going twin pregnancies with 32 reduced pregnancies in a single unit, the authors found no difference in outcomes be- tween the cohorts. 8 However, this study was underpowered, given the small numbers in both the study and the control groups used. In addition, fetal reduction is not without risks. In a recent large study, the complete loss rate prior to 24 weeks in pregnancies reduced from 2 to 1 was 2.1%. 9 The purpose of this study was to compare the risks of adverse pregnancy outcomes between ongoing twin preg- nancies and twin pregnancies reduced to singleton pregnancies in a single practice. From Maternal-Fetal Medicine Associates, PLLC (all authors), and the Department of Obstetrics, Gynecology, and Reproductive Science, Icahn School of Medicine at Mount Sinai (Drs Gupta, Fox, Klauser, and Rebarber), New York, NY. Received March 3, 2015; revised May 6, 2015; accepted June 3, 2015. The authors report no conflict of interest. Presented at the 35th annual meeting of the Society for Maternal-Fetal Medicine, San Diego, CA, Feb. 2-7, 2015. Corresponding author: Simi Gupta, MD. simikgupta@gmail.com 0002-9378/$36.00 ª 2015 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.ajog.2015.06.018 580.e1 American Journal of Obstetrics & Gynecology OCTOBER 2015 SMFM Papers ajog.org