Prolactin is a hormone produced by the pituitary gland, located at the base of the brain. Its most recognized function is the stimulation and maintenance of breast milk production (lactation) after childbirth. Prolactin also plays a significant role in reproductive health. When its levels become abnormally elevated, a condition called hyperprolactinemia occurs. This hormonal imbalance interferes with the normal signals required for conception, disrupting the precise hormonal rhythm and leading to problems with ovulation.
Prolactin’s Natural Suppression of Fertility
The body naturally uses high prolactin levels as a mechanism to suppress fertility immediately following delivery. This phenomenon is known as lactational amenorrhea, where the high concentration of the hormone prevents the return of the menstrual cycle. Infant suckling stimulates the pituitary gland to release prolactin, which is necessary for milk synthesis. This continuous, frequent stimulation keeps prolactin levels elevated, acting as a natural, though not entirely guaranteed, contraceptive. This physiological adaptation helps space out pregnancies. As the frequency and intensity of suckling decrease, the prolactin levels eventually fall, allowing the normal reproductive cycle to resume.
How High Prolactin Levels Block Ovulation
Elevated prolactin impairs fertility by disrupting the hormonal chain of command that controls the menstrual cycle. The primary target of the excess prolactin is the hypothalamus, inhibiting the pulsatile release of Gonadotropin-Releasing Hormone (GnRH). GnRH is the master signal that tells the pituitary gland to release Luteinizing Hormone (LH) and Follicle-Stimulating Hormone (FSH). By suppressing GnRH, high prolactin levels indirectly prevent the proper secretion of LH and FSH, which are essential for stimulating the ovarian follicles to mature and release an egg. This suppression leads to anovulation (failure to release an egg), the direct cause of infertility. The resulting hormonal environment can also manifest as irregular or absent menstrual periods (amenorrhea) and a milky discharge from the nipples (galactorrhea).
Identifying the Underlying Causes of Hyperprolactinemia
When high prolactin levels occur outside of pregnancy or breastfeeding, the condition is termed pathological hyperprolactinemia, which has several potential origins. The most common pathological cause is a prolactinoma, a benign (non-cancerous) tumor of the pituitary gland that produces excess prolactin. These tumors are typically classified by size, with microprolactinomas being smaller than 1 centimeter and macroprolactinomas being larger.
Another significant group of causes involves certain prescription medications that interfere with the regulation of prolactin. Since the brain chemical dopamine naturally suppresses prolactin release, any drug that blocks dopamine receptors can cause prolactin levels to rise. This includes some antipsychotic medications, certain anti-nausea drugs, and specific high blood pressure medications.
Systemic diseases can also contribute to elevated prolactin levels by affecting hormone clearance or regulation. For example, primary hypothyroidism (an underactive thyroid gland) can indirectly increase prolactin because the resulting elevated Thyrotropin-Releasing Hormone (TRH) also stimulates prolactin secretion. Chronic kidney disease can cause hyperprolactinemia because the kidneys are responsible for the clearance and breakdown of prolactin from the body.
Clinical Diagnosis and Treatment for Fertility Restoration
The diagnostic process for suspected hyperprolactinemia begins with a blood test to measure the serum prolactin level. This measurement is typically taken in the morning after a period of rest, to minimize temporary elevation caused by stress or venipuncture. Before confirming a diagnosis, doctors rule out physiological causes like pregnancy and screen for other endocrine issues, such as hypothyroidism.
Once hyperprolactinemia is confirmed, the primary goal of treatment is to restore normal prolactin levels and reproductive function. The most effective treatment for prolactinomas and most pathological cases involves medications called dopamine agonists, such as bromocriptine or cabergoline. These drugs mimic the action of dopamine, suppressing the pituitary’s production and release of prolactin.
Normalizing prolactin levels often restores the pulsatile release of GnRH, allowing the pituitary to resume normal LH and FSH production, ultimately leading to the return of ovulation and fertility. For patients with very large prolactinomas that do not respond to medication, surgical removal of the tumor or radiation therapy may be considered. Medical therapy is highly successful, often shrinking prolactinomas and restoring reproductive cycles in the majority of patients.