Prolactin is produced by the pituitary gland and is best known for driving milk production after childbirth. Its second, less well-known job is suppressing ovulation — the body's built-in way of spacing pregnancies during breastfeeding.
Why it matters outside of breastfeeding
Prolactin can also rise for other reasons: stress, certain medicines, an underactive thyroid, or a small benign pituitary growth. It can then suppress ovulation the same way. This shows up as a missed or late period, longer cycles, or spotting between periods. Nipple discharge unrelated to pregnancy can also occur, but it's often not the first or only sign.
How it's checked
A simple blood test measures the level. If the first result is high, the test is usually repeated in the morning, fasting and calm. Stress, and even the blood draw itself, can raise it for a short time. What the confirmed number means, and whether it needs treatment, depends on your symptoms and other test results — never on the number alone.