The relationship between endometrial thickness and outcome of medicated frozen embryo replacement cycles

ObjectiveTo examine the relationship between endometrial thickness and outcome of medicated frozen-thawed embryo replacement (FER) cycles.DesignA retrospective observational study.SettingAssisted conception unit at a university hospital.Patient(s)All patients who underwent an FER cycle between 1997 and April 2006 and met the inclusion criteria.Intervention(s)For endometrial preparation, a daily dose of 6 mg of oral E2 valerate was started on menstrual day 1, and P pessaries (800 mg daily) were administrated when the endometrial thickness had reached 7 mm or more, with ET taking place 2–3 days later. The FER cycles were categorized according to endometrial thickness measurement on the day of P supplementation.Main Outcome Measure(s)Implantation, clinical pregnancy, ongoing pregnancy, and live birth rates.Result(s)In all, 768 consecutive medicated FER cycles were analyzed. The lowest pregnancy rates were associated with endometrial thickness <7 mm (n = 13) and >14 mm (n = 12; 7% in both groups). Significantly higher implantation (19% vs. 12%), clinical pregnancy (30% vs. 18%), ongoing pregnancy (27% vs. 16%), and live birth (25% vs. 14%) rates were achieved in cycles where endometrial thickness was 9–14 mm (n = 386), compared with those in which endometrial thickness was 7–8 mm (n = 357). These differences remained significant after adjusting for confounding variables (adjusted odds ratio [OR] = 1.83 [confidence interval {CI} = 1.3–2.6] for clinical pregnancy, 1.8 [CI = 1.2–2.6] for ongoing pregnancy and 1.9 [CI = 1.3–2.8] for live birth).Conclusion(s)In medicated FER cycles, an endometrial thickness of 9–14 mm measured on the day of P supplementation is associated with higher implantation and pregnancy rates compared with an endometrial thickness of 7–8 mm.