Neonatal and maternal outcome after blastocyst transfer: a population-based registry study

Previous studies have shown a higher risk of birth defects and preterm birth (PTB) in singletons born after blastocyst transfer as compared to singletons born after cleavage-stage transfer. Few studies have investigated the maternal outcomes.

We sought to analyze the neonatal and maternal outcome after blastocyst transfer (day 5-6) compared to transfer of cleavage-stage embryos (day 2-3) and spontaneous conception.

This was a population-based retrospective registry study including all singleton deliveries after blastocyst transfer in Sweden from 2002 through 2013. The in vitro fertilization register was cross-linked with the Swedish Medical Birth Register, the Register of Birth Defects, and the National Patient Register. Deliveries after blastocyst transfer were compared with deliveries after cleavage-stage transfer and deliveries after spontaneous conception. Outcome measures included birth defects, PTB, low birthweight, small for gestational age, large for gestational age, perinatal mortality, placenta previa, placental abruption, and preeclampsia. Crude and adjusted odds ratios (AOR) with 95% confidence interval (CI) were calculated. Adjustment was made for year of birth of child, maternal age, parity, smoking, body mass index, years of involuntary childlessness, and child's sex and, for cleavage stage, also for number of oocytes retrieved, number of embryos transferred, and fresh/frozen embryo transfer.

There were 4819 singletons born after blastocyst transfer, 25,747 after cleavage-stage transfer, and 1,196,394 after spontaneous conception. Singletons born after blastocyst transfer had no increased risk of birth defects compared to singletons born after cleavage-stage transfer (AOR, 0.94; 95% CI, 0.79-1.13) or spontaneous conception (AOR, 1.09; 95% CI, 0.92-1.28). Perinatal mortality was higher in the blastocyst vs the cleavage-stage group (AOR, 1.61; 95% CI, 1.14-2.29). When comparing singletons born after blastocyst transfer to singletons born after spontaneous conception, a higher risk of PTB (<37 weeks) was seen (AOR, 1.17; 95% CI, 1.05-1.31). Singletons born after blastocyst transfer had a lower rate of low birthweight (AOR, 0.83; 95% CI, 0.71-0.97) as compared to cleavage-stage transfer. The rate of being small for gestational age was lower in singletons born after blastocyst transfer as compared to both cleavage-stage and spontaneous conception (AOR, 0.71; 95% CI, 0.56-0.88 and AOR, 0.70; 95% CI, 0.57-0.87, respectively). The risk of placenta previa and placental abruption was higher in pregnancies after blastocyst transfer as compared to pregnancies after cleavage-stage (AOR, 2.08; 95% CI, 1.70-2.55 and AOR, 1.62; 95% CI, 1.15-2.29, respectively) and spontaneous conception (AOR, 6.38; 95% CI, 5.31-7.66 and AOR, 2.31; 95% CI, 1.70-3.13, respectively).

No increased risk of birth defects was found in singletons born after blastocyst transfer. Perinatal mortality and risk of placental complications were higher in the blastocyst group as compared to the cleavage-stage group, observations that need further investigations.