The ovaries are the primary source of estrogen and progesterone in women of reproductive age, but they aren’t the only source. The adrenal glands, fat tissue, placenta (during pregnancy), and even the testes in men all contribute to production of these hormones. Where they come from depends on your sex, age, and whether you’re pregnant.
How the Ovaries Produce Both Hormones
Inside each ovary, developing egg follicles contain two distinct cell layers that work together to make estrogen. The outer layer (theca cells) responds to a brain signal called luteinizing hormone, or LH, by producing androgens. The inner layer (granulosa cells) then converts those androgens into estradiol, the most potent form of estrogen, using an enzyme called aromatase. This teamwork is sometimes called the “two-cell, two-gonadotropin” model because it requires two cell types and two pituitary hormones: LH and follicle-stimulating hormone (FSH).
Progesterone enters the picture after ovulation. Once an egg leaves its follicle, the leftover follicle cells transform into a temporary structure called the corpus luteum. This structure’s main job is producing progesterone, which thickens the uterine lining to prepare for a possible pregnancy. The corpus luteum also makes some estrogen. If no pregnancy occurs, it breaks down about 10 days after ovulation, progesterone drops, and a period follows. A new corpus luteum forms with every ovulation cycle, and the luteal phase during which it’s active lasts roughly 14 days.
The Brain Controls the Timing
The ovaries don’t act on their own. A region of the brain called the hypothalamus releases gonadotropin-releasing hormone (GnRH) in pulses. Those pulses tell the pituitary gland, a pea-sized structure at the base of the brain, to release FSH and LH into the bloodstream. FSH stimulates follicles to grow and mature. LH triggers ovulation and the formation of the corpus luteum. Rising estrogen and progesterone levels then feed back to the brain, dialing GnRH up or down depending on where you are in your cycle. This feedback loop is the reason hormonal birth control works: synthetic hormones trick the brain into thinking ovulation has already happened, so it stops sending the signals that trigger it.
The Placenta During Pregnancy
If sperm fertilizes the egg, a hormone called human chorionic gonadotropin (hCG) rescues the corpus luteum from breaking down. HCG is detectable in maternal blood about one day after implantation, roughly eight days after ovulation. It keeps the corpus luteum producing progesterone for the first 10 weeks or so of pregnancy.
After that point, the placenta takes over. By 10 to 12 weeks of gestation, it becomes the dominant source of progesterone. At full term, the placenta produces around 250 milligrams of progesterone per day, pushing blood levels to 100 to 200 ng/mL. It also produces large amounts of estrogen, using precursors supplied by the fetus. This shift from ovary to placenta is called the “luteal-placental shift,” and it’s why early pregnancy loss can occur if the corpus luteum fails before the placenta is ready.
Fat Tissue and the Adrenal Glands
The adrenal glands, which sit on top of the kidneys, produce small amounts of estrogen, progesterone, and androgens. In reproductive-age women, this adrenal contribution is a minor fraction of total production. But fat tissue plays a bigger role than many people realize. Fat cells contain aromatase, the same enzyme found in granulosa cells, and they use it to convert adrenal androgens into estrone, a weaker form of estrogen.
This conversion becomes especially important after menopause. Once the ovaries stop releasing eggs and the corpus luteum no longer forms each month, ovarian estradiol and progesterone production drops dramatically. Estrone, made primarily in fat tissue from adrenal precursors, replaces estradiol as the body’s main circulating estrogen. The conversion rate increases with age and with greater body fat, which is one reason higher body weight is associated with higher estrogen levels in postmenopausal women.
Estrogen Sources in Men
Men produce estrogen too, just in smaller amounts. In the testes, Leydig cells (the same cells responsible for testosterone) express aromatase and actively convert testosterone into estradiol. Developing sperm cells also synthesize estrogen and may actually be the largest source of it within the male reproductive tract. Estrogen in men helps regulate Leydig cell function and plays a role in maintaining the tubes that transport sperm out of the testes. Men also produce small amounts of estrogen through the same fat-tissue and adrenal pathways that operate in women.
How Levels Change Across Life Stages
In premenopausal women, estradiol fluctuates widely across the menstrual cycle. Levels peak just before ovulation, typically reaching 30 to 350 pg/mL, though values as high as 750 pg/mL have been reported. Progesterone stays low during the first half of the cycle, then surges after ovulation as the corpus luteum kicks in, before dropping again if pregnancy doesn’t occur.
After menopause, estradiol levels fall well below premenopausal ranges. Progesterone production from the ovaries essentially stops because ovulation no longer occurs and no corpus luteum forms. The adrenal glands continue producing trace amounts, but not enough to maintain the uterine cycling that defined the reproductive years. This decline in both hormones is what drives common menopausal symptoms like hot flashes, changes in bone density, and vaginal dryness.
In men, estradiol levels are generally lower than in premenopausal women but remain relatively stable across adulthood, gradually increasing slightly with age as body fat tends to increase and aromatase activity rises along with it.