Abstract: Objective · To compare the pregnancy outcomes between the patients undergoing single embryo transfer and double embryo transferin vitro fertilization and embryo transfer, and analyze the influencing factors. Methods · Jan. 2011 to Jun. 2016, women who underwent single embryo transfer or double embryo transfer with in vitro fertilization and embryo transfer and successfully conceived in Shanghai Ninth People′s Hospital, Shanghai Jiao Tong University School of Medicine were followed up to the pregnancy outcomes. According to the number of embryo transfer, the patients were divided into single embryo transfer group and double embryo transfer group. Univariate analysis (t test, Chi-square test) and multivariate Logistic regression analysis were used to compare the pregnancy outcomes between two groups, and analyze the influencing factors of adverse outcomes. Results · A total of 19 030 patients (98.69%) were followed up to the pregnancy outcomes. Stratified analysis showed that there were significant differences in the composition of pregnancy outcomes (P0.000) and the number of live births (P0.000) between two groups. For the neonatal birth quality, the infants bornthe patients with single embryo transfer had higher birth weights than those bornthe patients with double embryo transfer (P0.000), and the proportions of newborns with low birth weights and full-term newborns with low birth weights were higher among the patients with double embryo transfer compared to those with single embryo transfer (P0.000). In addition, there was no statistically significant difference in he incidence of birth defects between the infants bornthe patients with single embryo transfer and double embryo transfer. Multivariate Logistic regression analysis showed that the risk of abortion or labor induction among the patients with double embryo transfer was higher than those with single embryo transfer with age, infertility causes and embryo type adjusted (OR0.88, P0.025). Conclusion · The risk of adverse pregnancy outcomes is higher among the patients with double embryo transfer than those with single embryo transfer.

Key words: in vitro fertilization and embryo transfer (IVF-ET), single embryo transfer, double embryo transfer, pregnancy outcome, influencing factor