relationship of number of embryos transferred with perinatal outcome of singleton pregnancy

background: singleton pregnancy with a live birth beyond 37 weeks of gestation is the ultimate goal of any assisted reproductive technology. however, singletons conceived after art are found to have a poor perinatal outcome in comparison to naturally conceived singletons. it was hypothesized that the outcome of singleton conceived after transfer of two or more embryos may be dependent on the sharing of uterine space with other embryos. methods: patients who had single gestational sac visualized at 6 weeks after transfer of 4, 3 or 2 embryos were considered for the study. 195 singleton pregnancies were selected for final evaluation such that as per implantation rates of 25%, 33%, and 50%, they were divided into 3 groups of 50, 82 and 63 cases, respectively. the basic characteristics of pregnancy (gestational age, birth weight) were compared using analysis of variance (continuous variables), and categorical variables were evaluated with chi-squared test. the p<0.05 was considered statistically significant. results: among the various variables including maternal age, conception, type of infertility, type of abortion, total live birth, gestational age in live birth, birth weight, kind of embryo transfer and gestational age, there was not significant statistical differences between groups except gestational age that it was higher in group with 50% (p<0.04) implantation rate. therefore, higher number of initial embryos may affect the perinatal outcome of singleton conceived subsequently. conclusion: there is higher chance of missed abortion in patients with singleton pregnancies conceived after multiple embryo transfer. gestational age at delivery and birth weight were correlated with number of embryo transfered.