Endometrial Injury and Single Embryo Transfer

Inclusion Criteria: * woman age under 35 years * history of primary infertility * normoresponder (antral follicle count 5-10 in one ovary in early follicular phase * having grade I or II embryos for transfer * agree to undergo endometrial biopsy during the COH cycle. All patients were stimulated with luteal phase long protocol. Exclusion Criteria: * endocrinopathies (including diabetes mellitus, hyperprolactinemia, Cushing's disease, and congenital adrenal hyperplasia), any systemic disease, collagen disorder, hypercholesterolemia, sickle cell anemia, and a history of neoplasm; -high risk for or history of OHSS * using any concurrent medication (e.g., insulin-sensitizing drugs, and GnRH antagonists) * patients who did not proceed to follicle retrieval * severe male infertility requiring TESA/TESA * mullerian tract anomalies * a history of endometrial instrumentation or surgery within a month of the study * not agree to undergo endometrial biopsy during the COH cycle.