How do Ovulation Predictor Kits (OPK's) Work?
At the beginning of each menstrual cycle, a part of the female brain known as the hypothalamus produces the hormone GnRH (gonadotropin releasing hormone), which causes another part of the brain called the anterior pituitary gland to produce the hormones FSH (follicle stimulating hormone) and LH (luteinizing hormone). Both FSH and LH (to a lesser extent) travel to the ovaries and stimulate the development of multiple follicles (which each should contain an egg or oocyte) to develop.
As the follicles develop (and the eggs inside of them mature), the hormone estradiol (E2) is produced in increasing amounts. E2 travels back to the brain to control the production of GnRH, FSH, and LH. FSH does most of the work at this point, and initial LH production is relatively low.
However, E2 levels continue to rise and rise. Eventually, they become so high that the brain produces a surge of LH. LH travels to the ovaries and triggers ovulation (the release of a mature egg from its follicle in the ovary) to occur roughly 24-36 hours later.
Ovulation predictor kits (OPKs) rely on LH levels in the urine. These kits often consist of paper strips or devices similar to a pregnancy test. When a woman believes she’s close to ovulating, she can urinate on these strips and they will determine if the LH levels in her urine are high (positive) or low (negative). Once the results are high, she is expected to ovulate within 24-26 hours. Each doctor may have his or her instructions for when a couple should have intercourse following a positive result. Keep in mind that sperm can remain alive in the female reproductive tract for a few days, so daily intercourse is not always required.
