Progesterone is a steroid hormone that plays a central regulatory role in the female reproductive system. Primarily produced by the corpus luteum in the ovary following ovulation, it prepares the body for a potential pregnancy. Progesterone thickens the uterine lining, known as the endometrium, to make it receptive for a fertilized egg. Progesterone is also generated by the adrenal glands in both sexes, and its production dramatically increases in the placenta once a pregnancy is established.
Measuring Progesterone Levels
The quantity of progesterone is most commonly determined through a serum blood test. This measurement provides a snapshot of the circulating hormone level. Results are typically reported in nanograms per milliliter (ng/mL) in the United States, although some international laboratories use nanomoles per liter (nmol/L).
The timing of the test is a factor in interpreting the results, especially for non-pregnant individuals. To confirm that ovulation has occurred, the test is usually scheduled for the mid-luteal phase, approximately seven days after ovulation. A sufficiently high result during this window indicates that the corpus luteum is functioning as expected.
Normal Progesterone Levels Across the Lifespan
Progesterone levels change significantly depending on the phase of the menstrual cycle, the presence of pregnancy, and age.
Menstrual Cycle Levels
During the follicular phase (before ovulation), levels remain very low, typically less than 1 ng/mL. Following ovulation, the corpus luteum secretes progesterone, causing a sharp rise in the luteal phase. Normal ranges generally fall between 5 and 20 ng/mL. A level above 10 ng/mL is often considered sufficient to support a healthy uterine lining and confirm ovulation.
Pregnancy Levels
If conception occurs, progesterone levels continue to increase to maintain the pregnancy. During the first trimester, levels can range from approximately 11.2 to 90 ng/mL. As the pregnancy progresses, the placenta takes over hormone synthesis, leading to further increases in concentration. Second-trimester levels often range from 25.6 to 89.4 ng/mL, while the third trimester sees the highest concentrations, ranging from 48 to over 300 ng/mL. This volume is necessary to prevent uterine contractions and support fetal development.
Post-Menopause and Male Levels
In individuals who have reached menopause, the ovaries cease regular progesterone production, and levels drop to a low baseline, typically remaining below 1 ng/mL. Males also maintain a low level of progesterone, usually less than 1 ng/mL, where the hormone acts as a precursor for other steroids.
Causes and Implications of Abnormal Levels
Deviations from the expected ranges can signal underlying health conditions or reproductive challenges.
Low Progesterone
A consistently low progesterone level in the mid-luteal phase often points to a problem with ovulation or the corpus luteum’s function, known as a luteal phase defect. This deficiency can include irregular or heavy menstrual bleeding and difficulty achieving or maintaining a pregnancy. In a developing pregnancy, low progesterone is associated with an increased risk of miscarriage or ectopic pregnancy. Low levels can stem from anovulation (where an egg is not released), chronic stress, or underlying issues such as hyperprolactinemia, which disrupts the balance of sex hormones.
High Progesterone
Levels that are higher than the expected range outside of pregnancy or therapeutic use can also be a sign of specific conditions. Elevated progesterone may be caused by certain types of ovarian cysts or, in rare instances, by adrenal cancer or congenital adrenal hyperplasia. High levels are often less symptomatic than low levels, but they can sometimes mimic premenstrual syndrome symptoms like fatigue, bloating, and breast tenderness.
Therapeutic Uses and Dosages
Progesterone is administered therapeutically to supplement the body’s natural production, with the dosage and route varying based on the medical need.
Fertility Support
For fertility support, particularly in assisted reproductive technology (ART) cycles like in vitro fertilization (IVF), high doses are used to prepare the uterine lining for embryo implantation. Common regimens for luteal phase support include:
- 100 mg progesterone vaginal inserts two or three times daily.
- A total daily dose of 600 to 800 mg of vaginal progesterone.
- Intramuscular injections of progesterone in oil, typically 50 to 100 mg daily.
Hormone Replacement Therapy (HRT)
For postmenopausal individuals taking estrogen as part of HRT, progesterone is added to protect the uterus lining from overgrowth. This protection is achieved with lower, continuous oral doses, such as 100 mg daily, or cyclic dosing, such as 200 mg daily for 12 to 14 days each month.
Contraception
Progestins, which are synthetic compounds with progesterone-like effects, are the basis of many hormonal contraceptives. These are used at much lower, continuous doses to prevent ovulation and thicken cervical mucus. The specific dosage and formulation of progesterone are always individualized based on the patient’s condition, the route of administration, and the desired clinical outcome.