Relationship between endometrial thickness and embryo implantation based on 1,294 cycles of in vitro fertilization with transfer of two blastocyst-stage embryos

Objective: To evaluate the relationship between endometrial thickness and clinical outcome of IVF and ET. Design: Retrospective study. Setting: Private assisted reproductive technology center. Patients: One thousand two hundred and ninety-four infertility patients. Interventions: IVF and fresh autologous ET of two blastocyst-stage embryos, including at least one good-quality blastocyst. Main Outcome Measures: Clinical pregnancy rate (PR) and spontaneous abortion rate. Results: Endometrial thickness was greater in cycles resulting in pregnancy than in cycles not resulting in pregnancy (11.9 vs. 11.3 mm, respectively). Clinical pregnancy rates increased gradually from 53% among patients with a lining of < 9 mm, to 77% among patients with a lining of >= 6 mm. Multiple logistic regression analysis indicated significant effects of age, embryo quality, and endometrial thickness on both clinical pregnancy rates and live-birth or ongoing pregnancy rates. There was also a marginally significant trend toward decreasing rates of spontaneous pregnancy loss with increasing endometrial thickness. Conclusions: Clinical pregnancy and live-birth or ongoing pregnancy rates increase significantly with increasing endometrial thickness, independent of the effects of patient age and embryo quality.