EP25.15: Uterine contractility profiles differ in fresh versus frozen embryo transfer cycles in IVF/ICSI patients

Does uterine contractility differ according to IVF treatment protocol on the day of embryo transfer (ET) in the stimulated versus natural cycle? This ongoing multi-centre prospective observational cohort study investigating uterine contractility on transvaginal ultrasound (TVUS). Our study included patients undergoing IVF/ICSI treatment with good quality TVUS recordings and sonographically normal uteri in participating centres from 2017 to 2023. ET of good quality embryos in the blastocyst stage was performed. Six IVF/ICSI patients undergoing frozen embryo transfer (FET) patients were included from Embryolab Fertility Clinic in Thessaloniki Greece. Patients underwent elective freeze all treatment, after a GnRH agonist trigger. They then underwent modified natural cycle endometrial preparation with luteal support. 16 women underwent fresh ET IVF/ICSI treatment in the Ghent University Hospital. Pituitary downregulation was performed using either an agonist or an antagonist protocol. Women were treated with intravaginal progesterone starting on the day of HCG injection for luteal support. All patients underwent an TVUS measurement of uterine contractility within 1 hour prior to ET. Uterine contraction features were measured by applying dedicated speckle tracking and strain analysis. The 2 groups had comparable demographic characteristics and IVF indications. Frozen ET patients had a higher contraction frequency (1.64 vs 1.28 contractions/minute, p < 0.001), a higher contraction velocity (0.78 vs. 0.58 mm/sec, p = 0.036), and reduced contraction coordination (0.38 vs. 0.26 MSE, p = 0.032). Uterine contraction features are different in frozen natural cycle versus fresh stimulated cycle at ET, suggesting an effect of hormonal stimulation protocol. At time of ET during a fresh transfer cycle uterine contractility seems less active than in a natural cycle with frozen transfer.