Does atosiban before embryo transfer improve the chance of having a baby? A small trial reported higher clinical pregnancy rates, but that outcome is different from live birth. Larger randomized evidence has not established a clear overall live-birth benefit, and results need to be interpreted for the population and treatment studied.
Clinical pregnancy was reported in 58% of the atosiban group versus 38% with standard FET. These were two randomized groups, rather than a before-and-after change in the same patients.
- 20 percentage-point difference in clinical pregnancy rate between groups in a randomized trial presented at ESHRE in 2026
- Biological rationale: suppressing uterine contractions to facilitate embryo attachment… Limitations of a 100-patient single-center study
- Large-scale 1,100-patient RCT showed no statistically significant difference in live birth rates
Among patients undergoing In Vitro Fertilization (IVF), some receive an injection called atosiban shortly before embryo transfer. In patient communities, it is commonly referred to as a “uterine contraction suppression shot” or an “implantation shot.” Patients are told that dampening uterine movement right before transfer helps the embryo implant stably, but how much it truly increases the chances of pregnancy has long remained ambiguous.
However, a randomized controlled trial presented at this year’s Annual Meeting of the European Society of Human Reproduction and Embryology (ESHRE) demonstrated a significantly higher clinical pregnancy rate in women treated with atosiban compared to controls, putting the drug back under the clinical spotlight. Still, because the study cohort was small and earlier large-scale trials failed to confirm a definitive increase in live birth rates, it is premature to conclude that this medication benefits all fertility patients.
What did the 100-woman trial find?
Researchers from a fertility center in New Delhi, India, randomized 100 women undergoing frozen embryo transfer (FET) between February and September 2025 into two equal groups. The participants were aged 23 to 35, had a body mass index (BMI) under 30, possessed a normal uterine cavity, and exhibited an endometrial thickness of at least 7 mm. All patients underwent the transfer of two good-quality blastocysts.
Fifty women received 6.75 mg of intravenous atosiban 30 minutes before embryo transfer, while the remaining 50 underwent standard frozen embryo transfer.
The findings were striking: the clinical pregnancy rate—confirmed by ultrasonography after a positive serum β-hCG test—reached 58% in the atosiban cohort compared to 38% in the control group, a 20 percentage-point difference that the abstract reported as statistically significant (P < 0.05).
The implantation rate was also higher in the atosiban group at 33.3% versus 23.8% in controls—an absolute difference of approximately 9.5 percentage points—though this gap did not reach statistical significance (P = 0.12). Early first-trimester miscarriage rates were reported as 17.2% in the atosiban group and 21.1% in the control group, another numerical difference that was not statistically significant. The abstract does not give the calculation denominators for these miscarriage or implantation percentages, so they should not be read as percentages of all 50 women in each group.
Why might atosiban affect uterine contractions?
Atosiban is an oxytocin receptor antagonist. It acts by blocking the action of oxytocin—which stimulates uterine contractions—thereby dampening the mechanical motility of the myometrium.
The theoretical rationale behind using atosiban is that if the uterus contracts excessively at the moment of embryo transfer, the transferred embryo may be displaced from its optimal position or prevented from establishing stable apposition against the endometrial lining. Indeed, past observational studies have suggested that a higher frequency of uterine peristalsis and contractions during embryo transfer correlates with reduced clinical pregnancy rates.
In particular, a 2016 randomized trial in 120 women with endometriosis reported a clinical pregnancy rate per cycle of 58.3% following atosiban administration compared to 38.3% in controls, alongside a significant difference in implantation rates (41.0% vs. 23.4%).
The issue, however, is that research findings across the broader literature remain inconsistent.
What did the larger live-birth trial show?
When evaluating the true efficacy of atosiban, there is a landmark study that must be considered: a single-center, double-blind, placebo-controlled trial of 1,100 participants published in Human Reproduction in 2025.
That trial compared atosiban directly against placebo in women scheduled for a single frozen blastocyst transfer in an HRT cycle after one previous failed blastocyst transfer. On the most definitive clinical metric—the live birth rate—live birth occurred in 272/549 participants (49.5%) with atosiban versus 246/550 (44.7%) with placebo. The 4.8 percentage-point difference was not statistically significant (95% CI −1.1 to 10.7 percentage points; P = 0.10).
A prespecified subgroup included 163 women with abnormal contractions: more than four waves per minute or fundus-to-cervix waves at any frequency. Live birth was 51.9% (41/79) with atosiban versus 39.3% (33/84) with placebo—a 12.6 percentage-point difference (95% CI −2.6 to 27.8; P = 0.11), not a statistically significant benefit. Contractions were assessed in only 720 of 1,100 participants after a protocol amendment.
Ultimately, this suggests that rather than serving as a blanket medication needed by all patients, further targeted research is required to determine whether atosiban specifically benefits individuals with documented uterine hyper-peristalsis or distinct underlying causes of implantation failure.
What remains uncertain before using atosiban?
The trial presented at ESHRE draws attention because it was conducted as a randomized trial under well-defined frozen embryo transfer conditions and observed a substantial difference in clinical pregnancy rates.
Nevertheless, significant methodological limitations remain: the trial was conducted at a single center and enrolled only 100 participants. Furthermore, the study population was restricted to women with a relatively favorable baseline prognosis—aged 23 to 35, normal uterine cavities, endometrial thickness >= 7 mm, and receiving two top-grade blastocysts. These findings cannot simply be extrapolated to women of advanced maternal age or patients suffering from recurrent implantation failure (RIF). The authors themselves emphasized the need for larger, multicenter randomized trials.
For patients, a central outcome is whether treatment leads to a live birth, beyond a positive pregnancy test or ultrasound-confirmed pregnancy. The 100-woman abstract does not report live birth or child-health outcomes.
Therefore, based on the totality of current evidence, rather than branding atosiban as “the shot that boosts implantation if taken before transfer,” it is more accurate to describe it as an adjunct intended to reduce uterine contractions, with uncertain live-birth benefit. The large trial did not remeasure contractions after dosing, so it did not establish whether changes in contractions explained the outcomes.
For patients navigating IVF, the meaningful question is not simply “Should I get an atosiban shot?”, but rather “Is uterine hyper-contractility an actual identified issue in my case, and is there an expected clinical benefit to adding atosiban?”
While the 58% figure from this latest trial is undeniably eye-catching, a single small-scale study does not mean that every embryo transfer will see its success rate climb by 20 percentage points.
Another question to discuss before FET is whether to wait a cycle after egg retrieval before frozen embryo transfer. That timing decision is separate from whether to add atosiban.
※ This article was written based on research presented at the 2026 Annual Meeting of the European Society of Human Reproduction and Embryology (ESHRE) and published in the July 2026 Supplement of Human Reproduction (Volume 41, Supplement 1): “Atosiban administration before frozen embryo transfer is associated with higher clinical pregnancy rates: a randomized controlled trial” (Presentation L26/P-504, Abstract deag083.837, DOI: 10.1093/humrep/deag083.837). It does not replace individualized clinical diagnosis or medical care, and specific pharmaceutical decisions should always be made in consultation with a qualified reproductive specialist.
Additional primary sources: He et al., endometriosis trial (Fertility and Sterility, 2016); Cai et al., 1,100-participant trial (Human Reproduction, 2025), with its citation correction. The correction did not change the trial’s analyses or results.
※ Image: AI generated (ChatGPT, OpenAI) / For illustrative reference only.