Progesterone

What Progesterone Measures

Progesterone comes mainly from the corpus luteum, the structure a ruptured follicle turns into once it releases an egg.^[1] Before ovulation, follicular-phase levels stay low because there's no corpus luteum yet to make it. Small amounts also come from the adrenal glands, and during pregnancy the placenta eventually takes over most production.^[1] Because the corpus luteum is short-lived, a progesterone level is really a snapshot of whether that structure formed and is still active, which is why the hormone tracks the luteal phase so closely.

How It's Measured

Serum progesterone is measured directly from a blood draw and reported in ng/mL.^[1] It can also be tracked indirectly through urine, since the body breaks progesterone down into a metabolite called pregnanediol-3-glucuronide (PdG), which at-home urine tests read from a first-morning sample instead of a blood draw.^[5] Some labs also offer a salivary progesterone panel, though blood and urine are the two routes most people encounter.

Why People Track Progesterone

Progesterone is the hormone that turns the uterine lining from a growing tissue into a secretory one, thickening it and making it receptive in case a fertilized egg arrives.^[2] It also acts on the hypothalamus to raise the body's temperature set point, which is why basal body temperature runs a bit higher for the rest of the cycle once ovulation happens.^[3] Because it only shows up in meaningful amounts once the corpus luteum forms, a rise in progesterone is one of the clearest after-the-fact signs that ovulation occurred that cycle.

For how progesterone moves alongside estradiol and LH across a full cycle, see our hormone curve explainer.

How Go Go Gaia Tracks Progesterone

Go Go Gaia doesn't run lab tests itself, but you can upload a serum progesterone result or log an at-home PdG urine test, and the app charts either one against your logged cycle day and phase. That makes it possible to see where a reading fell relative to ovulation and your period, without lining up dates by hand.

What the Research Shows

In a study that tracked healthy women overnight with Oura rings across full cycles, nocturnal heart rate and body temperature were both higher during the mid- and late-luteal phases than during menses, while heart rate variability (rMSSD) tended to run lower in those same phases.^[4] Progesterone is the leading explanation for that pattern, since it's the dominant hormone once the corpus luteum forms and researchers point to its thermogenic effect as the mechanism behind the temperature rise.^[3] For more on those downstream signals, see Luteal Phase and HRV.

Because a blood draw isn't always practical for repeated testing, researchers have also studied urinary progesterone as an alternative way to confirm that ovulation happened. A 2018 study compared automated urinary progesterone assays against the standard PdG method and found that the automated readings could reliably distinguish the follicular phase from the luteal phase, supporting urine testing as a workable substitute for serial blood draws.^[5]

Related Terms

Frequently Asked Questions

Educational information based on published sources. Not medical advice. For personal concerns, please consult your doctor.

Why does progesterone rise after ovulation?

After an egg releases, the follicle it came from reorganizes into the corpus luteum, a temporary hormone-producing structure. The corpus luteum's main job is secreting progesterone, so the hormone climbs through the luteal phase and falls again if the corpus luteum breaks down near the end of the cycle.^[1]

What's the difference between a serum progesterone test and a PdG urine test?

A serum test measures progesterone directly from a blood draw, reported in ng/mL. A PdG test measures pregnanediol-3-glucuronide, the metabolite left over after the body breaks progesterone down, from a urine sample. Both are used to look at luteal-phase hormone patterns, but they're measuring different molecules through different routes.^[5]

Does progesterone affect body temperature?

Yes. Progesterone has a thermogenic effect, meaning it nudges core body temperature upward, which is why basal body temperature tends to run higher during the luteal phase than the follicular phase. That shift is what BBT tracking is built around.^[3]