Clinical pregnancy and live birth increase significantly with every additional blastocyst up to five and decline after that: an analysis of 16,666 first fresh single-blastocyst transfers from the Society for Assisted Reproductive Technology registry
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Stephanie Smeltzer, M.D., Kelly Acharya, M.D., Tracy Truong, M.D., Carl Pieper, M.D., Suheil Muasher, M.D.
To study the association between the number of blastocysts available and pregnancy outcomes in first fresh autologous single blastocyst transfer cycles.
Retrospective cohort study.
Patients from the Society for Assisted Reproductive Technology reporting fertility clinics (n=16,666).
Main Outcome Measure(s)
Primary outcomes were clinical pregnancy (CP), live birth (LB), and miscarriage rates. Logistic regression was used to investigate the association between the number of blastocysts and each outcome.
When comparing fresh single blastocyst transfer rates, the odds of a positive pregnancy outcome (CP) increased significantly with each additional supernumerary blastocyst up to five and declined by 2% for every additional blastocyst after five. Similarly, the odds of an LB was 17% higher for each additional blastocyst up to five and declined by 2% for every additional blastocyst after five. There was no significant association between blastocyst number and miscarriage rate.
Odds of positive pregnancy outcomes (CP, LB) increased significantly with every additional blastocyst up to five, but declined after that, in first fresh autologous cycles with single-blastocyst transfer. The decline after five may be explained by a detrimental effect on endometrial receptivity in patients with a large number of oocytes or inadequate selection of the best embryo for transfer based on morphology alone.