The continued push towards eliminating twin pregnancy: the clinical impact of the 2017 ASRM embryo transfer guidelines

To evaluate the differences in twin birth rates before and after implementation of the 2017 ASRM guidelines which limits the number of embryos transferred. Retrospective cohort study. Prior to April 2017, ASRM guidelines allowed for the transfer of 2 embryos in women under the age of 38 after the failure of an initial single embryo transfer. The new guidelines altered that recommendation to limit the transfer of 2 embryos only after the failure of multiple embryo transfer cycles in good prognosis patients. Our clinic, by policy, will not transfer more embryos than the ASRM guidelines, making it an ideal data set to analyze the impact of these guideline changes. We analyzed women under 38 years old in the two years before and after the national guideline change. The primary outcome was twin live birth. Only women on their second embryo transfer cycle were included. PGT and donor oocyte cycles were excluded. Published SART data was also compared between 2016 and 2017, to assess for national changes in the twin birth rate in patients under 38 years old. Differences in twin clinical pregnancy and live birth rates were compared by chi square test. Logistic regression controlled for embryo quality. Statistical significance was assumed at P<0.05. 367 live births in women under 38 years old with one prior embryo transfer were analyzed. The number of embryos in these patients was significantly reduced from 1.38 per patient to 1.0 after implementation of the new guidelines (P=0.001). This resulted in a significant reduction in the clinical twin pregnancy rate (14.2% vs 2.5%, P<0.001) and twin live birth rate (12.5% vs 2.5%, P=<0.001). There were no higher order multiple gestations. Despite the reduction in the number of embryos transferred, there was no change in the overall live birth rate per transfer in this patient group at 46.9% before and 50.3% after the policy change (P=0.31). The percentage of transfers with a good quality embryo increased from 61% to 67% over this time frame. Live birth remained similar before and after the 2017 guidelines even after adjustment for embryo quality (P=0.52). National SART data also showed a reduction in twin live births when comparing 2016 to 2017. In over 90,000 cumulative retrieval cycles in patients under 35 years old, the twin rate decreased from 16.5% to 13.3% (P<0.001). In over 50,000 cumulative retrieval cycles in patients 35-37 years old, the twin rate decreased from 15.6% vs 12% (P< 0.001). The SART data was less dramatic in the twin reduction, likely because it was not limited to patients with a prior cycle. Implementation of the 2017 ASRM guidelines decreased the twin rate in good prognosis women in our clinic and at a national level. Good prognosis women under 38 years old benefit from single embryo transfer, even if it is not their first embryo transfer.