Key Benefits

• Confirm ovulation happened and your body’s progesterone supports implantation.
• Spot anovulation or low post-ovulation support behind irregular cycles or spotting.
• Guide fertility planning by confirming when ovulation occurred in your cycle.
• Support early pregnancy assessment when paired with ultrasound and pregnancy tests to gauge viability.
• Protect fertility care by guiding progesterone supplementation during IVF or luteal support.
• Flag abnormal hormone production from ovarian or adrenal sources when levels are unexpectedly high.
• Track cycle trends over months to clarify patterns affecting conception or symptoms.
• Best interpreted 7 days after ovulation and alongside pregnancy tests and symptoms.

What is Progesterone?

Progesterone is a natural steroid hormone (a progestogen) made primarily by the ovary after ovulation in the corpus luteum. During pregnancy, the placenta becomes the dominant source, and smaller amounts are produced by the adrenal glands—and in men, by the testes and adrenals. It is synthesized from cholesterol via pregnenolone and circulates throughout the body to deliver signals to reproductive tissues, the brain, and other organs.

Its central job is to prepare and maintain the uterine lining (endometrium) for implantation and to support early pregnancy. Progesterone quiets uterine contractions, thickens cervical mucus, and works with estrogen to time the menstrual cycle’s luteal phase. It also influences temperature regulation and neural activity through a neuroactive metabolite (allopregnanolone). It helps shape immune tolerance to the embryo and serves as a precursor in the steroid pathway (steroidogenesis). In testing, progesterone serves as a readout of ovulation, luteal function, and placental hormone output.

Why is Progesterone important?

Progesterone is the body’s “settling” hormone. Made mainly after ovulation by the corpus luteum and by the placenta in pregnancy, it stabilizes the uterine lining, quiets smooth muscle, calms the brain via GABA pathways, raises basal temperature, modulates immunity, and balances estrogen’s growth signals across tissues.

In cycling women, levels are lowest before ovulation, surge after ovulation, and peak mid‑luteal; “optimal” sits in the middle‑to‑upper part of the luteal range for that phase. Pregnancy brings very high values. Men and postmenopausal women have low, steady levels.

When values are low during the luteal window, it often reflects weak or absent ovulation. The endometrium becomes estrogen‑dominant and unstable, leading to spotting, heavier or irregular bleeding, shorter cycles, and difficulty with implantation or early pregnancy loss. Many feel sleep disturbance, anxiety, or irritability from less GABAergic tone, and more cramping due to less smooth‑muscle relaxation. Low luteal progesterone is common in early teen years and perimenopause; low is expected after menopause and in men.

Higher values are normal right after ovulation and in pregnancy, where progesterone maintains uterine quiescence and immune tolerance. Outside these contexts, unusually high levels can arise from ovarian luteal cysts, adrenal sources, or medications, and may bring sleepiness, breast tenderness, bloating, constipation, fluid retention, and a small rise in body temperature.

Big picture: progesterone is the counterweight to estrogen, a signal of healthy ovulation, and a neurosteroid. Over time, adequate cyclic exposure protects the endometrium, supports fertility and mood stability, and links ovarian, adrenal, immune, and brain health.

What Insights Will I Get?

Progesterone is a steroid hormone made after ovulation by the corpus luteum and, in pregnancy, by the placenta. It stabilizes the uterine lining, signals that ovulation occurred, and coordinates the luteal phase. System-wide, it acts as a neurosteroid that calms GABA pathways, raises body temperature and ventilatory drive, relaxes smooth muscle, modulates fluid balance by opposing aldosterone, and shapes immune tolerance—especially important in early pregnancy.

Low values usually reflect anovulation or inadequate luteal function in cycling women, leading to unstable endometrium (spotting, short cycles), reduced fertility, and symptoms of unopposed estrogen such as breast tenderness or fluid retention. In early pregnancy, values low for gestational age can indicate insufficient corpus luteum or placental support. Low levels are expected after menopause and in males; when accompanied by low cortisol/androgens, they can point to reduced adrenal or pituitary drive.

Being in range suggests that ovulation occurred and luteal support is adequate, with a stable endometrium, predictable cycles, and steadier mood and sleep. In cycling women, optimal tends to sit mid-to-high within the luteal reference interval. In pregnancy, appropriately rising levels signal placental function. In males and postmenopausal women, low steady values are normal.

High values usually reflect the normal mid‑luteal peak or pregnancy. Outside those contexts, they can arise from luteal cysts, ovarian or adrenal sources, or exogenous progestins, and may cause sedation, bloating, breast tenderness, and higher body temperature. In males, high progesterone can suppress gonadotropins and lower testosterone.

Notes: Interpret by context—cycle timing (mid‑luteal vs follicular), pregnancy stage, and assay type. Many immunoassays cross‑react with progestins; LC‑MS/MS is more specific. Hormonal contraception and fertility treatments alter results.