Ovulation disorders (40 percent)
	Aging
	Diminished ovarian reserve
	Endocrine disorder (e.g., hypothalamic amenorrhea, hyperprolactinemia, thyroid disease, adrenal disease)
	Polycystic ovary syndrome
	Premature ovarian failure
	Tobacco use
Tubal factors (30 percent)
	Obstruction (e.g., history of pelvic inflammatory disease, tubal surgery)
Endometriosis (15 percent)
Other (about 10 percent)
Uterine/cervical factors (more than 3 percent)
	Congenital uterine anomaly
	Fibroids
	Polyps
	Poor cervical mucus quantity/quality (caused by smoking, infection)
	Uterine synechiae