What blood test can be helpful in determining if a female patient is ovulating regularly?

The measurement of progesterone levels around day 21 of the menstrual cycle is a key indicator of ovulation, particularly in females with a typical 28-day cycle. After ovulation, the corpus luteum forms and secretes progesterone, which helps to prepare the uterine lining for potential implantation of a fertilized egg. A day 21 progesterone level, therefore, reflects whether ovulation has occurred, as progesterone peaks approximately a week after ovulation.

If the progesterone level is elevated, it suggests that ovulation has taken place, as the body has produced this hormone in response to the corpus luteum's activity. Conversely, low levels would indicate that ovulation either did not occur or that it is not occurring regularly, thus making this test a useful tool in assessing a patient's ovulatory status.

The date of the last menstrual period can provide context regarding the menstrual cycle but does not directly measure ovulation. The follicle-stimulating hormone level is more indicative of ovarian reserve and function rather than confirming ovulation. While a luteinizing hormone assay can indicate the surge that triggers ovulation, it does not confirm that ovulation has actually occurred, as it only reflects a temporary spike rather than the subsequent progesterone secretion that confirms