Elective single versus double blastocyst-stage embryo transfer in women aged 36 years or older: a retrospective cohort study.

We evaluated if elective single-blastocyst transfer (eSBT) could be adopted in women aged 36 or older. In this retrospective cohort, women aged ≥36 years received IVF ovarian stimulation cycles and had ≥ two blastocysts. A total of 240 women underwent eSBT and 189 double-blastocyst transfer (DBT) in the first transfer cycle. The subsequent frozen-thawed embryo transfer cycles were a combination of single- and double- blastocyst transfers. Analysis was stratified for patients in age groups 36-37, 38-39 and ≥40, considering the quality of the blastocyst transferred. The cumulative live birth rates (cLBR) were 74.2% (178/240) versus 63.0% (119/189) after eSBT versus DBT, respectively (aOR: 1.09 (0.68, 1.75)). Time to live birth did not vary significantly between the two groups (HR: 0.85 (0.68, 1.08)). The total number of children born was 194 after eSBT (162 singletons and 16 pairs of twins) versus 154 (84 singletons and 35 twins) after DBT. The odds ratios for preterm birth (0.37 (0.21-0.64)), and low birth weight (0.31 (0.16, 0.60)) were all lower in eSBT. In women aged ≥36 years, cLBR following single- versus double- blastocyst transfer was comparable while the odds of multiple live births and adverse perinatal outcomes were reduced.