Prospective evaluation of endometrial thickness as a predictor of pituitary down-regulation after gonadotropin-releasing hormone analogue administration in an in vitro fertilization program.

Objective: To determine whether pituitary down-regulation after gonadotropin-releasing hormone analogue (GnRH-a) administration can be accurately predicted by transvaginal ultrasonographic measurement of endometrial thickness.

Design: Prospective study.

Setting: An IVF unit of an academic medical center.

Patient(s): One hundred eighty-one patients undergoing 265 IVF-ET treatment cycles using GnRH-a in the long protocol.

Main Outcome Measure(s): Serum concentrations of E2 were determined, and endometrial thickness was measured by transvaginal sonography. The accuracy of endometrial thickness for predicting pituitary down-regulation was calculated.

Result(s): Pituitary down-regulation, defined as a serum E2 concentration of < or = 55 pg/mL, was achieved in 77% (204 of 265) of the cycles. An endometrial thickness of < or = 6 mm was found in 92.2% (188 of 204) of cycles in which down-regulation was achieved. An estradiol level of < or = 55 pg/mL was present in 95.9% (188 of 196) of cycles with endometrial thickness of < or = 6 mm.

Conclusion(s): A state of relative hypoestrogenism after GnRH-a administration, indicative of pituitary down-regulation, can be predicted with a high degree of accuracy by ultrasonographic measurement of endometrial thickness. Thus, routine testing for serum E2 concentration may be safely omitted. This may allow further simplification of IVF protocols and increase both cost-effectiveness and patients' convenience.