Obstetrical and Neonatal Outcomes of in vitro Fertilization Twins after Fresh Embryo Transfer versus Frozen-Thawed Embryo Transfer

Abstract

<b><i>Objectives:</i></b> The limited data regarding obstetrical outcomes in multiple pregnancies following both fresh embryo transfer and frozen-thawed embryo transfer (FET), along with the association between multiple pregnancies and increased pregnancy complications compared to singleton pregnancies, highlight the need for research on this topic. Therefore, this study aimed to compare obstetrical and neonatal outcomes of twin pregnancies after fresh embryo transfer versus FET. <b><i>Design:</i></b> This was a retrospective single-center study. <b><i>Participants:</i></b> There were in vitro fertilization (IVF) dichorionic twin pregnancies ≥23 weeks of gestation during 2010–2022. <b><i>Setting:</i></b> This retrospective study was based on data recorded at Galilee Medical Center, a tertiary-care university-affiliated hospital, Israel. <b><i>Methods:</i></b> We conducted a comparative analysis of obstetrical and neonatal outcomes between IVF dichorionic twin pregnancies after fresh embryo transfer and those after FET. This analysis included variables such as gestational age at delivery, birthweight, preterm birth rates, low birthweight rates, neonatal intensive care unit admissions, and complications related to prematurity. <b><i>Results:</i></b> The study included 389 IVF twin pregnancies: 253 after fresh embryo transfer and 136 after FET. Following fresh embryo transfer compared to FET, the mean gestational age at delivery was earlier (34 + 6 vs. 35 + 5 weeks, <i>p</i> = 0.001) and the rate of preterm birth (&lt;37 weeks) was higher (70.4% vs. 53.7%, <i>p</i> = 0.001). This difference in gestational age at delivery remained significant after adjustment for maternal age, parity, and BMI (OR = 2.11, 95% CI: 2.11–3.27, <i>p</i> = 0.001). Similarly, the difference in preterm birth rates remained significant after adjustment of the same variables (<i>p</i> = 0.001). For the fresh embryo transfer compared to the FET group, the mean birthweight was lower (2,179.72 vs. 2,353.35 g, <i>p</i> = 0.003); and low birthweight and very low birthweight rates were higher (71.2% vs. 56.3%, <i>p</i> &lt; 0.001 and 13.5% vs. 6.7%, <i>p</i> = 0.004, respectively). For the fresh embryo transfer compared to the FET group, the proportions were higher of neonates admitted to the neonatal intensive care unit (23.3% vs. 16.0%, <i>p</i> = 0.019), of neonates with respiratory distress syndrome (10.5% vs. 5.9%, <i>p</i> = 0.045) and those needing phototherapy (23.3% vs. 16.0%, <i>p</i> = 0.019). <b><i>Limitations:</i></b> Limitations of the study include its retrospective nature. Furthermore, we were unable to adjust for some confounders, such as the number of eggs retrieved, the number of embryos transferred, and methods for ovarian stimulation or preparation of the endometrium for embryo transfer. <b><i>Conclusions:</i></b> Obstetrical and neonatal outcomes of twin pregnancies were worse after fresh embryo transfer than after FET. The findings support favorable fetal outcomes after FET and support the current trend of shifting from fresh embryo transfer to FET. Prospective studies are needed to support our results.