An estrogen test measures the level of the most important estrogen hormones (estradiol, estriol, and estrone) in a blood or urine sample.
- Estradiol is the most commonly measured type of estrogen for nonpregnant women. The amount of estradiol in a woman’s blood varies throughout her menstrual cycle. After menopause, estradiol production drops to a very low but constant level.
- Estriol levels usually are only measured during pregnancy. Estriol is produced in large amounts by the placenta, the tissue that links the fetus to the mother. It can be detected as early as the 9th week of pregnancy, and its levels increase until delivery. Estriol can also be measured in urine.
- Estrone may be measured in women who have gone through menopause to determine their estrogen levels. It also may be measured in men or women who might have cancer of the ovaries, testicles, or adrenal glands.
Both men and women produce estrogen hormones. Estrogens are responsible for female sexual development and function, such as breast development and the menstrual cycle. In women, estrogens are produced mainly in the ovaries and in the placenta during pregnancy. Small amounts are also produced by the adrenal glands. In men, small amounts of estrogens are produced by the adrenal glands and testicles. Small amounts of estrone are made throughout the body in most tissues, especially fat and muscle. This is the major source of estrogen in women who have gone through menopause.
For pregnant women, the level of estriol in the blood is used in a maternal serum triple or quadruple screening test. Generally done between 15 and 20 weeks, these tests check the levels of three or four substances in a pregnant woman’s blood. The triple screen checks alpha-fetoprotein (AFP), human chorionic gonadotropin (hCG), and a type of estrogen (unconjugated estriol, or uE3). The quad screen checks these substances and the level of the hormone inhibin A. The levels of these substances-along with a woman’s age and other factors-help the doctor estimate the chance that the baby may have certain problems or birth defects.