Obstetric and Perinatal Outcomes of Pregnancies Resulting from Fresh Versus Frozen Embryo Transfer-a Sibling Cohort.

We aimed to compare obstetric and perinatal outcomes of in vitro fertilization (IVF) pregnancies following fresh and frozen embryo transfer (FET). This was a historic cohort of deliveries between November 2008 and January 2020 at a single university hospital, in which each fresh transfer IVF pregnancy was matched to a FET pregnancy by the same woman (1:1 ratio). We included live singleton deliveries (> 24 weeks of gestation) and excluded pregnancies following egg donation. The primary outcome was birthweight, and secondary outcomes were small for gestational age (SGA) neonates and preterm birth (PTB). A total of 107 fresh transfer pregnancies were matched to 107 FET pregnancies, in the same women. Mean maternal age was lower in the fresh transfer group compared to the FET group (30.4 vs. 32.5 years, p < 0.001). A higher rate of nulliparity was noted in fresh transfer pregnancies (64.5% vs. 12.1%, p < 0.001). Mean birthweight was non-significant between the groups (p = 0.13), and the rates of low birthweight and small for gestational age neonates did not differ between the groups. Preterm deliveries occurred in 10.3% and 9.3% of fresh transfer and FET pregnancies respectively, p = 0.79. On multivariate linear regression analysis, the type of embryo transfer-FET or fresh-was not independently associated with birthweight, after adjustment for women's age, nulliparity, and BMI. IVF pregnancies following fresh and FET entailed the same obstetric and perinatal outcomes when compared in the same women.