Pmn-19: A Comparison of Neonatal Outcomes following Transfer of Frozen and Fresh Embryo

Background: Currently, frozen embryo transfers contribute an increasing rate of births from assisted reproductive technologies such as in vitro fertilization (IVF). However, very few studies evaluated the neonatal outcomes from frozen embryo transfer. This study aimed to investigate and compare the neonatal outcomes from frozen embryo transfer versus fresh embryo transfers. Materials and Methods: This systematic review assessed more of 20 studies from books, articles and different sites of internet about the neonatal outcomes following transfers of frozen and fresh embryo in 1995- 2012. Results: Studies illustrated no significant difference between two kinds of embryo transfers in preterm birth rate and mode of delivery. However, the boys to girls ratio was 1.05 times higher in the frozen group. Low birth weight (LBW), small for gestational age (SGA) and prematurity were approximately twice higher in the fresh population. In another study compared intrauterine parameters of 910 singletons born after frozen embryo transfer (FET) with 9603 babies from fresh embryo transfer and 4656 naturally conceived (NC) children. The mean birth weight of the frozen babies was 134g higher compared to the fresh babies (p<0.0001). The rate of large for gestational age (LGA) babies was significantly different between the three groups with 16.9% for FET, 10.3% for fresh transfer and 11.4% for NC babies. The same applied to the rate of babies with birth weight of 4500gr or more (5.6%, 2.8% and 3.4% respectively). Conclusion: Frozen embryo transfer did not seem to adversely affect neonatal outcomes including prematurity, LBW and SGA and even birth weight in FET was higher because in FET cycles hormone supplementation mimics the natural cycle, compared to the super physiologically high hormonal stimulation of women in fresh cycles, this similarity to natural cycle in FET may influence endometrial receptivity, early implantation and placental development in a positive way, leading to fetal growth and higher mean weight.