Are perinatal outcomes affected by blastocyst vitrification and warming?

Transfer of cryopreserved-warmed embryos into an appropriately prepared uterus unaffected by controlled ovarian hyperstimulation is common in the practice of in vitro fertilization. There is limited information on the effect of blastocyst vitrification and warming on perinatal outcomes.

We sought to determine if perinatal outcomes are affected after the transfer of vitrified-warmed blastocysts compared to the transfer of fresh blastocysts, by comparing preeclampsia rate, birthweight, percentage of low birthweight, and preterm delivery rate between embryo transfer types.

We performed a retrospective database cohort study of 289 fresh and 109 vitrified-warmed blastocyst transfer cycles at an academic medical center. Cycles were performed from July 2, 2009, through Dec. 8, 2014, and included infants born at ≥20 weeks gestational age, excluding donor egg cycles. We examined the association between transfer type (fresh or vitrified-warmed) and proportion of deliveries complicated by preeclampsia, preterm delivery (gestational age <37 weeks), and low birthweight (<2500 g). We assessed associations using generalized linear models, both unadjusted and adjusted, for maternal age, newborn sex, diabetes status, and parity.

We observed more pregnancies complicated by preeclampsia following vitrified-warmed transfers (7.6%) compared to fresh embryo transfers (2.6%) (P = .023) (adjusted odds ratio, 3.1; 95% confidence interval, 1.2-8.4). Newborns resulting from vitrified-warmed embryo transfer cycles were similar to those resulting from fresh embryo transfer cycles with regard to low birthweight (7.4% vs 5.3%, P = .421), mean birthweight (3443 vs 3431 g, P = .865), and preterm delivery rate (9.2% vs 8.7%, P = .869).

We conclude that embryo vitrification with warming may affect some perinatal outcomes since preeclampsia is increased compared to fresh blastocyst transfer. However, other perinatal outcomes such as low birthweight and preterm delivery rate are not affected. Fresh blastocyst transfers should be considered when possible as they may reduce the incidence of preeclampsia.