Our aim was to determine prospectively whether increased body mass index (BMI) affects endometrial receptivity through displacement of the window of implantation (dWOI) using the endometrial receptivity analysis (ERA), and whether this effect is BMI-dependent. We recruited a population of 170 infertile women with a normal uterus and no clinical history of recurrent miscarriage or implantation failure. These women were divided into four groups according to BMI: normal weight (18.5-24.9 kg/m; n = 44), overweight (25-29.9 kg/m; n = 29), class I obese (30.0-34.9 kg/m; n = 54), and class II and III obese (> 35 kg/m; n = 43). We also assigned the patients to one of two larger BMI cohorts: non-obese (normal weight and overweight; n = 73) and obese (class I, II, and III obese; n = 97). We compared analytical and clinical data and dWOI in these categories, finding significant metabolic differences in glycemia, TSH, insulin, HDL cholesterol, LDL cholesterol, triglycerides, and systolic and diastolic blood pressure among the different BMI groups. One-day dWOI increased significantly with BMI, and significant differences were observed in the non-obese versus obese categories (9.7% vs 25.3 %, respectively (p = 0.02)). dWOI was most pronounced in patients with class II-III obesity. In addition, displacement was longer as BMI increased since ERA revealed a higher proportion of displacements of 1 day than of 12 h and showed they were predominantly pre-receptive. In conclusion, obesity has a negative effect on endometrial receptivity through delaying of the WOI, which increases in function of BMI as well as the metabolic disturbances of the patient.

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