Why Should You Care How Long Your LH Surge Lasts?
If you’re trying to get pregnant, you’ve probably developed a sudden new interest in monitoring the level of luteinizing hormone (LH) in your urine. LH is the hormone that tells your ovaries that it’s time to release an egg. Just before ovulation, levels of LH surge. How long your LH surge lasts is important, because this is your most fertile time—the time when having sex is most likely to result in a pregnancy.
How Do You Detect Your LH Surge?
You can detect levels of LH in your urine by peeing on sticks. These ovulation predictor kits (OPK) turn positive when you have a certain level of LH in your urine. A positive OPK usually means that you are currently in the midst of an LH surge, and you will ovulate in the next 12 – 24 hours. If you start testing a few days before you expect to ovulate, you can be confident that you’ll catch your surge and be able to have sex when your chances of conceiving are highest.
Well, that’s how OPKs work in theory. In practice, it’s not always that simple.When you take an OPK, you are getting a snapshot of your LH levels at one point in time, and it can be difficult to piece together a full picture of where you are in your cycle from your OPKs. You might get multiple days of positive OPKs in a row. Does that mean your LH surge lasts longer than normal? Or you might get almost-positives, but never a truly darker second line. Does that mean you never had an LH surge at all?
The LH surge lasts different amounts of time for different women.
It’s best to think of levels of LH in your body as a curve that changes throughout your cycle. In the typical cycle, LH starts out low, then rapidly rises and peaks a day or two before ovulation, then falls back down right after ovulation. But just as not every woman has a textbook 28-day cycle, not every woman has exactly the same LH curve.
A study in the journal Fertility and Sterility looked at how long the LH surge lasts in normally ovulating women. The image below represents what different LH patterns would look like on daily OPKs from cycle day 11 through cycle day 21 according to the results of the study:
As you can see from this chart, some LH surges are long, and others are short. If you happen to have a long LH surge, it doesn’t mean you are more fertile—it simply means you will get a few days of positive OPKs before you actually ovulate.
So…What Should You Do With This Information?
And if you happen to have a short LH surge, it doesn’t mean you are any less fertile—but it does mean you may have a harder time catching your LH surge using OPKs. You may need to test twice a day, since your window for getting a positive may be only a few hours.