In females, hormones are produced by a network of organs working together, with the ovaries, pituitary gland, hypothalamus, adrenal glands, and thyroid playing the largest roles. During pregnancy, the placenta becomes a major hormone producer as well. Even fat tissue and the pancreas contribute to the hormonal picture. Each of these sources has a distinct job, and they constantly communicate with one another through chemical signals in the blood.
The Hypothalamus Starts the Chain
The hypothalamus is a small region at the base of the brain that acts as the starting point for female reproductive hormone production. It releases a signaling molecule called gonadotropin-releasing hormone (GnRH) in rhythmic pulses. These pulses travel a short distance to the pituitary gland, where they trigger the release of two critical hormones that control the ovaries. The speed and frequency of these pulses determine which ovarian hormones get made and when, essentially setting the tempo for the entire menstrual cycle.
The hypothalamus also receives feedback from the hormones it helped create. When estrogen and progesterone levels rise, they signal the hypothalamus to slow down GnRH production, completing a negative feedback loop. Just before ovulation, however, rising estrogen flips this signal to positive feedback, prompting a surge that triggers egg release. This switch from “slow down” to “speed up” is one of the more remarkable features of female reproductive biology.
The Pituitary Gland Directs the Ovaries
Sitting just below the brain, the pituitary gland responds to GnRH by releasing two gonadotropic hormones: follicle-stimulating hormone (FSH) and luteinizing hormone (LH). FSH stimulates the ovaries to produce estrogen and supports egg development. LH triggers ovulation and then drives the production of progesterone in the second half of the menstrual cycle. Without adequate FSH and LH output, the ovaries cannot function properly, a condition called central hypogonadism that leads to problems with fertility and sexual development.
The Ovaries: Primary Source of Estrogen and Progesterone
The ovaries are the primary hormone-producing organs of the female reproductive system. They make three major forms of estrogen (estradiol, estrone, and estriol) along with progesterone and small amounts of androgens like testosterone. Estradiol is the most potent of the three estrogens during the reproductive years, and its levels fluctuate dramatically across the menstrual cycle: roughly 19 to 140 pg/ml during the follicular phase, peaking at 110 to 410 pg/ml just before ovulation, then settling to 19 to 160 pg/ml in the luteal phase.
Different cell types within the ovary handle different hormones at different times. During the first half of the cycle, the developing follicle produces most of the estradiol. Granulosa cells in the follicle also begin producing small amounts of progesterone just before ovulation. After the egg is released, the empty follicle transforms into a structure called the corpus luteum, which becomes the primary source of progesterone. Progesterone levels jump from 0.1 to 0.7 ng/ml in the first half of the cycle to 2 to 25 ng/ml in the second half. This surge prepares the uterine lining for a possible pregnancy, supports breast tissue development, and causes the slight rise in body temperature many women notice mid-cycle.
The Adrenal Glands Add Androgens
The two adrenal glands, which sit on top of the kidneys, produce a group of weak androgens from a region called the zona reticularis. These include DHEA, DHEAS, and androstenedione. On their own, these hormones have limited androgenic activity. Their real importance is as raw materials: they circulate through the bloodstream and get converted into more potent androgens like testosterone, or into estrogens like estradiol, in other tissues throughout the body.
The adrenal glands also release small amounts of progesterone as a byproduct of making other steroid hormones. This contribution is minor compared to ovarian output during the reproductive years, but it becomes more relevant after menopause when the ovaries are no longer active.
Fat Tissue as a Hormone Factory
Fat cells are not passive storage. Adipose tissue actively produces estrogen using an enzyme called aromatase, which converts adrenal androgens (primarily androstenedione) into estrone. In premenopausal women, this is a small supplement to ovarian estrogen. After menopause, it becomes the dominant source. Estrone synthesized in fat tissue is the main circulating estrogen in postmenopausal women.
This is why body composition matters for hormonal balance. In women with higher body fat, aromatase activity is greater, which can lead to higher estrogen levels. The relationship runs both ways: estrogen deficiency after menopause promotes fat accumulation, and excess fat tissue alters the expression of estrogen receptors and the enzymes involved in estrogen production.
The Placenta During Pregnancy
During pregnancy, the placenta takes over as a major hormone-producing organ. One of its first and most important products is human chorionic gonadotropin (hCG), the hormone detected by pregnancy tests. hCG rescues the corpus luteum from breaking down, keeping progesterone production going in early pregnancy. Placental hCG peaks between weeks eight and ten, then drops to a lower plateau for the rest of pregnancy.
By about 10 to 12 weeks, the placenta itself becomes competent to produce progesterone directly, taking over from the corpus luteum. By the time a pregnancy reaches full term, progesterone levels climb to 100 to 200 ng/ml, with the placenta churning out roughly 250 mg per day. The placenta also produces human placental lactogen (hPL), which is secreted primarily into the mother’s bloodstream and acts on maternal tissues to support the metabolic demands of pregnancy.
The Thyroid’s Influence on Hormonal Balance
The thyroid gland, located in the front of the neck, produces hormones (T3 and T4) that don’t directly control reproduction but significantly influence it. Thyroid hormones affect the synthesis, secretion, and clearance of reproductive hormones throughout the body. An overactive thyroid is associated with increased levels of total estradiol, testosterone, and progesterone, while an underactive thyroid tends to cause the opposite pattern.
Thyroid problems also disrupt prolactin, a pituitary hormone involved in breast milk production. About 40% of women with an underactive thyroid also have elevated prolactin levels, which can interfere with ovulation. Even in healthy women, normal fluctuations in T3 and T4 affect how estrogen and progesterone are metabolized across the menstrual cycle.
The Pancreas and Ovarian Function
The pancreas produces insulin, a hormone best known for regulating blood sugar. But insulin also directly affects the ovaries. When insulin levels are chronically elevated, as happens with insulin resistance, it stimulates ovarian cells to produce more androgens. This occurs both directly and indirectly, by boosting LH release and increasing the number of LH receptors on ovarian cells. This mechanism is central to polycystic ovary syndrome (PCOS), where excess insulin drives androgen overproduction, disrupting ovulation and causing symptoms like acne, excess hair growth, and irregular periods.
What Changes After Menopause
After menopause, the ovaries largely stop producing estradiol. Circulating estradiol drops by 85 to 90% from premenopausal levels, falling below 35 pg/ml. Estrone levels drop by 65 to 75%. The body doesn’t stop making estrogen entirely, though. Extragonadal sources take over: fat tissue, skin, bone, kidney, and even the brain all produce small amounts of estrogen locally. In postmenopausal women, estrogen production in fat tissue and bone cells is actually more active than in younger women, suggesting these localized sources play an important role in maintaining tissue-specific functions even after the ovaries go quiet.