Progesterone Test

This test measures levels of the hormone progesterone in the blood. Progesterone is a steroid hormone that is mainly secreted in the corpus luteum of the ovaries.

Progesterone plays a key role in determining phases of the menstrual cycle, monitoring fertility therapies, and helping to determine the cause of infertility. While a small amount of progesterone is produced in the adrenal gland, the majority is made in the ovaries by the corpus luteum. During the luteal phase (or second half) of the menstrual cycle, a rise in luteinizing hormone (LH) stimulates ovulation. The corpus luteum is subsequently formed and secretes progesterone which promotes the development of secretory endometrium.

Progesterone is required for the maintenance of pregnancy. It is initially secreted by the corpus luteum and then by the placenta after approximately 9-10 weeks gestation. Progesterone levels increase dramatically from the end of the first trimester to term.

Clinical Significance

• Disorders of the first trimester: Serum progesterone levels are occasionally used in a patient with bleeding to evaluate the possibility of miscarriage or of an ectopic gestation. The usual combination of tests includes serial serum hCG levels and progesterone concentration combined with ultrasound.
• Evaluation of infertility: Serum progesterone measured 1 week prior to the expected menses can be used to assess ovulation (eg, cycle day 21 in a 28-day menstrual cycle). A progesterone level > 3 ng/mL usually indicates ovulation.
• Assisted reproduction: The test is useful for monitoring patients having ovulation induction with hCG, hMG, FSH/LHRH, or clomiphene.