1. Extended embryo culture with single embryo transfer (SET) at the blastocyst stage resulted in more pregnancies and live births than transfer at the cleavage embryo stage.
2. Extended embryo culture was not associated with adverse obstetric or perinatal outcomes.
Evidence Rating Level: 2 (Good)
Study Rundown: This study found that single embryo transfer (SET) at the blastocyst stage (day 5) was associated with higher pregnancy and live birth rates compared to SET at the cleavage stage (day 2-3). Extended embryo culture time was not associated with adverse obstetric or perinatal outcomes. Inclusion of only single embryo transfers at one institution where identical embryologic protocols and culture medias were used allowed for a simple, elegant study design. Assessment of adverse outcomes is limited by low incidence in the study population and retrospective design further limits interpretation. Future investigations might employ a larger sample size and retrospective design to assess for differences in rates of adverse outcomes, including abnormal placentation and postpartum hemorrhage.
Study Author, Dr. Galia Oron, MD, talks to 2 Minute Medicine: Department of Obstetrics and Gynecology, McGill University
“Blastocyst transfer has several advantages, including a higher implantation rate than day three embryos and the ability to perform genetic testing. Since single blastocyst transfers are becoming more common, it is important to know whether extended time under culture conditions has any long-term negative effect on the resulting pregnancies and neonates.”
In-Depth [retrospective cohort study]: Researchers compared outcomes among 1543 autologous SETs in women ≤40 years old by whether transfer occurred at the single cleavage embryo stage (day 2-3) (n=693) or the fresh single blastocyst stage (day 5) (n=850). The primary outcomes included pregnancy and live birth rates as well as numerous obstetric and perinatal complications, including preeclampsia, placental abruption, low birth weight, preterm delivery, NICU hospitalization, and congenital malformations.
Blastocyst transfer was associated with a higher pregnancy rate (50.1% vs.19.9%, p<0.001) and a higher live birth rate (33.5% vs. 13.8%, p<0.001) than cleavage embryo transfer. There were no significant differences in pregnancy-related complications or adverse neonatal outcomes between the two groups after adjustments were made for known risk factors (maternal age, BMI, smoking, cause of infertility, parity, and gender).
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