The ovaries are the primary gland that produces progesterone. Specifically, a temporary structure called the corpus luteum forms inside the ovary after ovulation each month and serves as the body’s main progesterone factory. But the ovaries aren’t the only source. The placenta, adrenal glands, testes, and even the brain also produce progesterone in varying amounts depending on the circumstances.
The Corpus Luteum: Your Main Progesterone Source
Every month during the menstrual cycle, one of your ovaries releases an egg from a fluid-filled sac called a follicle. Once that egg escapes, the empty follicle doesn’t just disappear. It transforms into a yellow-tinted mass of cells called the corpus luteum, and this new structure immediately begins pumping out progesterone.
Making progesterone is the corpus luteum’s most important job. During the first half of your cycle (before ovulation), progesterone levels stay below about 2 ng/mL. After ovulation, the corpus luteum ramps up production dramatically. Levels peak roughly one week later, climbing to around 20 ng/mL. That surge prepares the uterine lining for a potential pregnancy by thickening it and increasing its blood supply.
If no pregnancy occurs, the corpus luteum breaks down after about 10 to 14 days. Progesterone drops, the uterine lining sheds, and your period begins. If sperm does fertilize the egg, the corpus luteum sticks around and keeps releasing progesterone for roughly 12 weeks to sustain the early pregnancy.
The Placenta Takes Over During Pregnancy
The corpus luteum can’t maintain progesterone production forever. Around the seventh week of pregnancy, the placenta begins producing substantial amounts of progesterone on its own. This transition, sometimes called the luteoplacental shift, gradually moves the job of progesterone production from the ovary to the placenta. By the end of the first trimester, the placenta is firmly in control.
From that point on, progesterone levels climb steadily. During the first trimester, levels range from about 11 to 44 ng/mL. By the second trimester, they rise to 25 to 83 ng/mL. In the third trimester, progesterone can reach 58 to 214 ng/mL, with some measurements as high as 300 ng/mL. These high levels keep the uterine lining stable, prevent contractions, and support fetal development throughout pregnancy.
The Adrenal Glands and Testes
Your adrenal glands, which sit on top of your kidneys, also produce small amounts of progesterone. In the adrenals, progesterone mainly serves as a building block. The gland uses it as a stepping stone to manufacture other steroid hormones, including cortisol (your body’s primary stress hormone). The amount of progesterone the adrenals release into the bloodstream is relatively minor compared to the ovaries, but it becomes the main source after menopause, when progesterone levels typically drop below 0.5 ng/mL.
In men, the testes produce progesterone through specialized cells called Leydig cells. Male progesterone levels are low, roughly comparable to what women have during the follicular phase. But the hormone still plays a functional role: it influences sperm development, helps sperm become capable of fertilizing an egg (a process called capacitation), and contributes to testosterone production.
Progesterone Made in the Brain
One of the more surprising production sites is the brain itself. Neurons and supporting brain cells contain the enzymes needed to manufacture progesterone locally, independent of the ovaries or adrenal glands. This locally produced progesterone acts as a “neurosteroid,” meaning it influences brain function directly at the site where it’s made.
Brain-derived progesterone promotes the growth of the protective coating around nerve fibers, called myelin. It stimulates the cells responsible for building that coating to mature and multiply, and it increases the percentage of nerve fibers that become properly insulated. This has implications for nerve repair after injury. Progesterone produced in the brain also appears to protect neurons from damage caused by low oxygen, and its byproducts play a role in pain signaling pathways.
What Controls Progesterone Production
The pituitary gland, a pea-sized structure at the base of your brain, orchestrates the whole process. It releases luteinizing hormone (LH), which triggers ovulation and stimulates the corpus luteum to produce progesterone. Without that LH signal, the corpus luteum wouldn’t form and progesterone wouldn’t spike during the second half of the cycle. Interestingly, a small rise in progesterone to about 0.5 ng/mL actually occurs just before ovulation and may itself help trigger the hormonal surge that causes the egg’s release.
This feedback loop between the pituitary and the ovaries means that anything disrupting LH production, whether stress, extreme weight changes, or pituitary disorders, can reduce progesterone output downstream.
Signs of Low Progesterone
When progesterone production falls short, the effects depend on whether you’re pregnant. In non-pregnant women, common signs include irregular periods, difficulty conceiving, headaches, mood changes (including anxiety or depression), trouble sleeping, hot flashes, and bloating or weight gain. Many of these overlap with other hormonal issues, which is why blood tests timed to specific points in your cycle are the standard way to check levels.
During pregnancy, low progesterone can cause spotting, breast tenderness, fatigue, low blood sugar, and in some cases, miscarriage. Progesterone supplementation is sometimes used in early pregnancy precisely because the corpus luteum is the sole source during those critical first weeks before the placenta is ready to take over.