Elective single embryo transfer in women less than age 38 years reduces multiple birth rates, but not live birth rates, in United States fertility clinics.

Objective: To determine the effect of elective single ET (eSET) on live birth and multiple birth rates by a cycle-level and clinic-level analysis.

Design: Retrospective cohort study.

Setting: Not applicable.

Patient(s): Patient ages <35 and 35-37 years old.

Intervention(s): None.

Main Outcome Measure(s): Clinics were divided into groups based on eSET rate for each age group and aggregate rates of live birth per ET and multiple birth per delivery were calculated. A cycle-level analysis comparing eSET and double ET (DET) live birth and multiple birth rates was also performed, stratified based on total number (2, 3, or 4+) of embryos available, embryo stage, and patient age.

Result(s): There was a linear decrease in multiple birth rate with increasing eSET rate and no significant difference in clinic-level live birth rates for each age group. Cycle-level analysis found slightly higher live birth rates with double ET, but this was mainly observed in women aged 35-37 years or with four or more embryos available for transfer, and confirmed the marked reduction in multiple births with eSET.

Conclusion(s): Our study showed a marked and linear reduction in multiple birth rates, and important, little to no effect on clinic-level live birth rates with increasing rates of eSET supporting the growing evidence that eSET is effective in decreasing the high multiple birth rates associated with IVF and suggests that eSET should be used more frequently than is currently practiced.