Progesterone is produced primarily by the corpus luteum of the ovary in normally menstruating women and to a lesser extent by the adrenal cortex. At approximately the 6th week of pregnancy, the placenta becomes the major producer of progesterone. The major functions of progesterone are in the preparation of the uterus for implantation and maintenance of pregnancy.
During the follicular phase of the cycle, progesterone levels remain low (0.2-1.5 ng/mL). Following the LH surge and ovulation, luteal cells in the ruptured follicle produce progesterone in response to LH. During this luteal phase, progesterone rises rapidly to a maximum of 10-20 ng/mL at 5 to 7 days following ovulation. If conception does not occur, progesterone levels decrease during the last four days of the cycle due to the regression of the corpus luteum. If conception occurs, the levels of progesterone are maintained at mid-luteal levels by the corpus luteum until about week six. At that time, the placenta becomes the main source of progesterone and levels rise from approximately 10-50 ng/mL in the first trimester to 50-280 ng/mL in the third trimester.
Serum progesterone is a reliable indicator of either natural or induced ovulation because of its rapid rise following ovulation. Disorders of ovulation, including anovulation, are relatively frequent and are responsible
for infertility in approximately 15-20% of patients. Progesterone levels are abnormally low in these patients during the mid-luteal phase. Luteal phase deficiency is a reproductive disorder associated with
infertility and spontaneous abortion and is thought to occur in 10% of infertile women. The infertility and pregnancy loss associated with this disorder are thought to be attributable to inadequate development of the
endometrium. The failure of the endometrium to mature is thought to be caused by insufficient production of progesterone by the corpus luteum.
Progesterone levels in the luteal phase are lower than normal in women with luteal phase deficiency.
Measurement of progesterone in the first 10 weeks of gestation has been shown to be reliable and effective for the diagnosis and treatment of patients with threatened abortion and ectopic pregnancy. Suppressed progesterone levels (5 to 25 ng/mL) in the presence of detectable amounts of hCG is highly suggestive of patients with threatened abortion or ectopic pregnancy, regardless of gestational age.
Manufacturer’s Reagent package insert Architect Progesterone, February 2016, Abbott Ireland Diagnostic Division, Lisnamuck, Longford Co.,Longford,Ireland