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 medication that was used to prevent miscarriage.

Speroff L, Fritz MA (2005). Clinical Gynecologic Endocrinology and Infertility, 7th ed. Adapted with permission from Lippincott Williams and Wilkins.

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.