Unexplained infertility was diagnosed according to standard World Health Organization (WHO) criteria. All women in the study had hormonal assessment to evaluate their ovulatory cycles, thyroid function, circulating prolactin and androgen levels. The ovarian reserve was checked by measurement of serum FSH and an antral follicle count on the third day of the menstrual cycle. Screening for infertility also included transvaginal ultrasound and hysterosalpingography, to exclude possible uterine malformations or pathologies, and to assess the patency of the fallopian tubes. Male factor infertility was excluded in all couples, according to standard WHO semen analysis.