Atosiban in Single Blastocyst Transfer in Patients With Previous Pregnancy Failure and Abnormal Uterine Contractions

Participants in the atosiban group will receive an intravenous bolus injection of atosiban (37.5 mg/5 mL, , Tractocile®，Ferring Pharma,Geneva, Switzerland) at a rate of 6.75 mg/0.9 mL 30 minutes prior to embryo transfer, followed by a 1-hour intravenous infusion at a rate of 18 mg/h. After 1 hour, the atosiban infusion rate will be reduced to 6 mg/h, with a total dose of 37.5 mg.

Participants in the placebo group will receive an identical saline infusion over the same timeframe. Specifically, saline will be administered intravenously 30 minutes prior to embryo transfer (ET), followed by a continuous intravenous infusion for one hour. This will be succeeded by a further continuous intravenous infusion of saline for 2.125 hours.