You may have heard of OPKs (ovulation predictor kits) before and wondered what exactly they are. Many women, without fully understanding what they are testing, purchase these when trying to conceive to supposedly predict the onset of ovulation in order to catch it in time to conceive that cycle. 

Firstly, OPK is a misnomer. As you’d heard before, *nothing can predict ovulation*. We can look at the signs, yes, and know that it is likely to occur soon. But so many interwoven factors influence the timing of ovulation, that no one thing can be 100%. This is why, in FAM, we never predict ovulation. Instead we look for the signs of it approaching, we assess whether we are fertile or infertile *today*, and we confirm ovulation only *retrospectively*. Because of our understanding of the biomarkers of fertility, we can still know a day’s fertility status even without pinpointing the exact moment of ovulation (only possible if caught on ultrasound). 

Instead of calling them OPKs, just know that these urine tests are simply LH tests. LH (see previous post) is luteinizing hormone. Previously, I’ve explained the role it plays in a very simplified form. However it’s actually so intricate, and some parts of LH’s production  and role in the cycle are still being learned and understood. Simply, LH surges prior to ovulation, which causes the follicle to rupture, thereby releasing the ovum (ovulation). LH then luteinizes the remaining follicle, transforming it into the corpus luteum which is the temporary endocrine gland that produces progesterone. That’s the simple explanation. 

LH actually doesn’t just surge (plateau) randomly out of nowhere mid-cycle. Instead it begins to increase slightly, along with FSH, at the end of the previous cycle, prior to menstruation. This is because at the end of the cycle, progesterone and estrogen both fall, and the inhibitory effect they have over FSH and LH via positive-feedback begins to diminish. At this point, FSH and LH start creeping up again, thereby beginning the processes of a new cycle even before menstruation has arrived. 

LH also doesn’t just rupture and luteinize follicles. It also plays a role in the actual production of estrogen in the ovaries. LH stimulates the theca interna cells that line the follicle to produce estrogens, which of course in turn cause the cervix to produce cervical mucus. LH helps to produce the very estrogens that then (via positive-feedback) cause LH to decrease after a certain point. Theca interna cells have receptors for LH which cause them to produce androstenedione. Androstenedione is a weak androgen steroid hormone required to manufacture estrogen (it’s an intermediary in the biosynthesis of both estrone and testosterone from DHEA or dehydroepiandrosterone). 

At some point around the peak of estrogen, LH does increase dramatically, signaling *likely* (not definite) impending ovulation within ~12-36 hours. This surge is thought to be caused by the sudden fall in estrogen that occurs right after it peaks around ovulation, however while the mechanism for the LH is not fully understood, it is known that the estrogen fall is definitely not the only cause. 

It’s around this point that the LH surge/plateau is detectable via urine tests, signaling the likely impending event of ovulation. Now, if you are trying to conceive, waiting until you see a positive LH test is rather late in the game to start unprotected intercourse. If you are charting your cycle, cervical mucus should give you a much earlier warning of when ovulation might occur. Know that in fertile (aka all) cervical mucus prior to ovulation, sperm can survive for up to 5 days. So you could have sex 5 days before ovulation, your cervical mucus would prepare the sperm to meet the egg, and then once ovulation happens the sperm would be ready and waiting to join with and fertilize the ovum. This gives you many days of advance notice, so you can optimize intercourse for conception. However, if you’re waiting for a positive LH before starting to try, you might have 1 or 2 days of opportunity before ovulation occurs. Cervical mucus can be detected without tests––just you and your body. 

So why bother LH testing at all? Well, in FAM we often appreciate cross-checks to confirm ovulation after the fact. For example, in the Symptothermal methods we use BBT to cross-check cervical mucus to confirm ovulation. In the same way LH can be just one more biomarker to use to confirm ovulation, and unlike BBT, yes, it does serve to give a little bit of an advance notice, similar to (but not as prolonged as) cervical mucus. For those who are instead using a Symptohormonal method with cervical mucus as the primary biomarker, LH testing can add a second cross-check where BBT is not used. In other words, many women feel that more biomarkers = more security and accuracy in charting. 

However, LH tests can never be the primary means of assessing ovulation or fertility in FAM. First of all, remember that all cervical mucus prior to confirmed ovulation is fertile. And remember that cervical mucus generally appears days before the LH surge. So LH can’t tell you when the fertile window is opening, because by the time it surges, you’ve already been fertile for days. Again, as mentioned, LH tests are not able to predict that ovulation is 100% about to happen, nor that it 100% did happen…only that it’s likely. You can see why LH testing alone would be very unhelpful for avoiding pregnancy!

Women with normal/healthy length (~24-36) ovulatory cycles, and relatively succinct windows of increasingly fluid cervical mucus, will likely find them to be most accurate. In some cycles, something calls LUFS (luteinized unruptured follicle syndrome) may occur, where everything looks to have occurred as intended, however the follicle containing the ovum never actually ruptured, even though it was luteinized by LH, thereby releasing progesterone and giving the appearance on charts of an ovulatory cycle (except that with LUFS, the luteal phase may extend beyond 18 days without a pregnancy). In this case, a woman would have seen a positive LH, but in actually ovulation never occurred. It’s not super common, but it can happen! 

Additionally, women with PCOS may also find LH testing to be less helpful. With PCOS, a woman has androgen excess, and her cycles are often seen to have multiple FSH launches, resulting in multiple POCs (points of change) that never result in ovulation. In this case, she may see multiple positive LH tests over the course of a very long cycle, but of course she wasn’t ovulating with every single positive LH test (ovulation can only happen once per cycle, and once it does, it will be followed by a luteal phase and subsequently menstruation within about 2 weeks on average).

By working with a trained FAM educator, you can learn when to use LH tests, and when to start and stop testing in a given cycle. You’ll also learn when they may not be the most helpful thing. LH testing is an optional additional biomarker, unlike cervical mucus which is absolutely necessary!


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