Objective: To investigate the effect of differences in endometrial thickness and pattern as visualized with present-day high-resolution transvaginal ultrasound equipment on the outcome of assisted reproductive treatment.
Design: Prospective cohort study.
Setting: Two large infertility units in university hospitals.
Patient(s): The endometrial characteristics of 981 patients during 1,600 assisted reproductive treatment cycles were compared with those of 205 untreated women. In addition, abnormal echogenic patterns of the endometrium were characterized histologically in 44 patients.
Intervention(s): None.
Main outcome measure(s): Pregnancy rates.
Result(s): The endometrium was significantly thinner in untreated women and women treated with IUI than in women treated with IVF or intracytoplasmic sperm injection. The exponential proliferation of the endometrium was similar in conception and nonconception cycles. The odds for a successful pregnancy were significantly lower in the presence of a thin endometrium in women treated with IUI but not in women treated with the long stimulation protocol for IVF or intracytoplasmic sperm injection. Singleton pregnancies were more common than multiple pregnancies in patients with thin endometria.
Conclusion(s): The pregnancy rates of assisted reproductive procedures are influenced only marginally by the degree of endometrial proliferation, and treatment should not be canceled because of inadequate endometrial thickness.