The Impact of Uterine Peristalsis on Clinical Pregnancy Rates in In Vitro Fertilisation (IVF): A Systematic Review and Meta-Analysis.

Uterine peristalsis - rhythmic, wave-like contractile activity of the subendometrial myometrium - has been proposed as a factor that may influence embryo implantation. Whether peristaltic frequency measured around the time of embryo transfer is associated with clinical pregnancy in in vitro fertilisation (IVF) remains incompletely resolved, and existing syntheses have pooled studies in which the exposure was not measured during the transfer cycle itself. We conducted a systematic review and meta-analysis in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) 2020 statement. Eligible studies were original, peer-reviewed observational studies of women undergoing IVF or intracytoplasmic sperm injection with embryo transfer, in which uterine peristaltic frequency was quantified by ultrasound during the embryo transfer cycle and clinical pregnancy was reported by peristalsis stratum. Reviews, conference abstracts, preprints, and studies of pharmacological interventions altering contractility were excluded. Risk of bias was appraised with the Risk Of Bias In Non-randomised Studies - of Exposures (ROBINS-E) tool, and certainty of evidence with the Grading of Recommendations Assessment, Development and Evaluation (GRADE) framework. Odds ratios (ORs) were pooled using DerSimonian-Laird random-effects models. Given the small anticipated evidence base, subgroup, funnel-plot, and sensitivity analyses were prespecified as exploratory. Four studies comprising 863 embryo transfer cycles and 371 clinical pregnancies met eligibility criteria. Clinical pregnancy occurred in 160 of 478 cycles (33.5%) with high uterine peristalsis and 211 of 385 cycles (54.8%) with low peristalsis. High peristaltic frequency was associated with approximately half the odds of clinical pregnancy (pooled OR 0.45, 95% confidence interval [CI] 0.32-0.62; P < 0.001), corresponding to 197 fewer clinical pregnancies per 1,000 cycles (95% CI 268 fewer to 120 fewer). Heterogeneity was low (I² = 19.8%; τ² = 0.023; Q = 3.74, df = 3, P = 0.29), although the 95% prediction interval (0.17-1.17) crossed unity. The association was robust to leave-one-out analysis (OR range 0.38-0.50) and to restriction to studies using a harmonised 2 waves/min threshold (OR 0.50, 95% CI 0.36-0.69; I² = 1.4%). Subgroup analyses by cycle type and exposure threshold showed no significant effect modification. Funnel plot asymmetry was not detected (Egger P = 0.27), though power was minimal. Certainty of evidence was very low. Elevated uterine peristaltic frequency measured during the embryo transfer cycle is consistently associated with substantially reduced odds of clinical pregnancy in IVF. However, the evidence derives from four small, unblinded observational studies using non-standardised, largely post hoc frequency thresholds assessed at differing times relative to transfer, and a prediction interval crossing unity indicates that a future study could plausibly find no association. Uterine peristalsis should be regarded as a promising but unvalidated prognostic marker; clinicians cannot currently alter management on the basis of peristalsis alone, and standardised measurement protocols and prospective evaluation against live birth are prerequisites for any clinical role.