O-029 Atosiban in women with previous single implantation failure undergoing frozen-thawed blastocyst transfer: a placebo-controlled randomized trial
Authors: Cai H , Liu S , Yang C , Chen L , Xie J , Ben W M , Wang M , Jia H , Li W , Shi J 
Published: July 2024

Abstract

Study question
Does the administration of Atosiban before frozen-thawed blastocyst transfer improve the live birth rate in women with a history of a single implantation failure?

Summary answer
In women with a single implantation failure undergoing frozen-thawed blastocyst transfer, Atosiban did not improve the ongoing pregnancy rate.

What is known already
Uterine peristalsis preceding embryo transfer is believed to adversely impact the success rates of IVF. Atosiban can reduce uterine peristalsis and act as a role of oxytocin antagonist. The effectiveness of Atosiban in the general population of IVF patients has not been conclusively shown by randomised clinical trials or meta-analyses. It has been suggested that women with previous implantation failure may potentially benefit from the use of Atosiban, particularly in the presence of uterine peristalsis. We aim to evaluate if Atosiban before embryo transfer increases live birth rate in women undergoing frozen-thawed blastocyst transfer?

Study design, size, duration
We conducted a single-centre, double-blind placebo randomised controlled trial (RCT) in women with previous single implantation failure undergoing frozen-thawed blastocyst transfer. Between July 2019 and June 2023, we randomised 1,100 participants to either Atosiban or placebo. The primary outcome was live birth (≥20 weeks of gestation) in the first FET after randomization. In this abstract, we present results on ongoing pregnancy. Data on live birth will be available at the conference.

Participants/materials, setting, methods
We randomised women with a history of one failed fresh or frozen blastocyst, with at least one cryopreserved blastocyst into two groups on the day of transfer. In the Atosiban group, women were administered 37.5mg of Atosiban intravenously 30-min prior to FET. In the placebo group, women received a saline infusion for the same duration. Uterine peristalsis was measured using transvaginal ultrasound prior to administration of study drugs. The analysis was done based on intention-to-treat.

Main results and the role of chance
The ongoing pregnancy rates were 50.46% (277/549) and 46.82% (258/551) in the Atosiban and control groups, respectively (RR 1.08, 95% CI 0.95 to 1.22, P = .23). Uterine peristalsis was measured in 720 (65%) of all participants. Within this cohort, of the 163 (22%) women with abnormal contractions, the ongoing pregnancy rates were 51.9% and 41.7%, respectively (RR 1.25, 95% CI 0.90 to 1.73, P = .19). Among 208 women (29%) with peristalsis but without abnormal contraction waves, ongoing pregnancy rates were 50.9% and 48.0% (RR 1.06, 95% CI 0.81 to 1.40, P = .67). In 349 women (48%) without peristalsis, the ongoing pregnancy rates were 48.6% in the Atosiban group versus 50.6% in the control group (RR 0.96, 95% CI 0.78 to 1.19, P = .71).

Limitations, reasons for caution
Our study only included women with previous blastocyst implantation failure. Uterine peristalsis was not initially assessed, resulting in only 65% (720/1,100) of the participants having peristalsis measured. In this abstract, we only report on the ongoing pregnancy rate. We will present data on live birth at the congress.

Wider implications of the findings
In unselected women undergoing frozen-thawed blastocyst transfer with previous single implantation failure, Atosiban does not enhance the ongoing pregnancy rate. Future research regarding Atosiban in IVF should assess uterine peristalsis and focus on women with abnormal contractions.

Trial registration number
ChiCTR1900022333