Analysis of Pregnancy Outcomes for The Vanishing Twin Syndrome in In Vitro Fertilization and Embryo Transfer

Objective The aim of this study was to assess the pregnancy outcomes after spontaneous reduction in in vitro fertilization and embryo transfer （IVF-ET） twin pregnancies. Methods A retrospective analysis of 632 cases clinical pregnancies after IVF-ET during 2015-2016 was conducted. Spontaneous reduction in twin pregnancies happened in 60 cases. Totally 129 cases of twin pregnancies without spontaneous reduction were analyzed as twin control group;443 cases with single pregnancy during the same period were analyzed as singleton control group. We analysis the incidence of spontaneous reduction in twin pregnancies, and compare the clinical pregnancy outcomes within these groups. Results The incidence of spontaneous reduction in IVF-ET twin pregnancies was 31.74%. The premature delivery rate（8.34% vs. 48.83%,χ²=29.168,P<0.01）, live birth rate （97.37% vs. 94.65%,χ²=8.513,P<0.01）, take-home baby rate（97.37% vs. 91.77%,χ²=8.621,P<0.01）, gestational age（38.6 weeks vs. 35.7 weeks,F=20.323,P<0.01） and birth weight（3.14 kg vs. 2.42 kg,F=32.231,P<0.01） in spontaneous reduction group were significantly better than those of twin control group. The miscarriage rate（31.66% vs. 21.89%,χ²=9.81,P<0.01） and cesarean rate（63.16% vs. 53.47%,χ²=10.296,P<0.01） were higher than those of singleton control group,but other pregnancy outcomes were not inferior to those of singleton control group. Conclusion The pregnancy outcomes of spontaneous reduction group are significantly better than those of the twin control group, but a little poorer than the singleton control group. We suggest the selective single embryo transfer, because it can decrease the disadvantageous effect of the multiple pregnancy rate and the spontaneous reduction, which may make benefit to the IVF patients.