Infertility has many causes that involve either the woman's, the man's, or both partners' reproductive systems. Some causes include:

• Problems with the man's reproductive system.
• Problems with the woman's fallopian tubes.
• Problems with the woman's uterus and/or cervix.
• Problems with ovulation.
• Uncommon problems such as the man or woman having been exposed before birth to DES, a medicine that was used to prevent miscarriage.

Rates of infertility and miscarriage increase with age. A woman's fertility peaks in her late 20s and gradually begins to decline in her early 30s. A more pronounced drop in fertility and increase in miscarriage risk begins around her mid-30s, primarily due to the aging egg supply. Male fertility also decreases with age but it is a more gradual decline than in women.