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For starters, the kits will tell you when your body is entering the peak baby-making phase.
This article originally appeared on Time.
If you’re hoping to become pregnant, ovulation prediction kits say they’ll tell you when your body is entering the peak baby-making phase of its monthly cycle. When they’re used properly, they really do work, experts say—and you have options about what type to use.
For years, the market for ovulation prediction kits has been dominated by urine-based tests that check for spikes in a woman’s levels of luteinizing hormone, or LH.
LH is always present, but it surges just before a woman’s mature egg passes through the wall of her ovary and makes its way down the fallopian tube to meet up with any eligible spermatozoa that happen to be around. When used correctly, LH tests are around 99% accurate, says Dr. Rene Leiva, an assistant professor of family medicine at the University of Ottawa and the Bruyère Research Institute. Leiva has conducted several studies on the pros and cons of home fertility monitoring methods.
But using them correctly can be a little tricky. For one thing, women need to use these LH kits first thing in the morning, before they’ve had a lot to eat or drink, to ensure reliable results. Also, a woman has to test herself at the appropriate time in her cycle. If she tests too early or too late, she may miss or fail to identify her LH surge. And it doesn’t work the same for everyone. Some women, including those approaching menopause or taking fertility-enhancing drugs, may not be able to rely on LH levels to predict ovulation, says Dr. Rebecca Flyckt, an OB/GYN at Cleveland Clinic. Sign up for and more view example
A point to remember is that LH kits do not signal the start of a woman’s fertile period—only that ovulation is roughly 24 hours away.
“The best studies show a woman’s fertile window is four to five days before ovulation,” Flyckt says. A man’s sperm can live for up to a week in a woman’s reproductive system, and it takes a little time—roughly six to 12 hours—for that sperm to make its way to where it can successfully fertilize the egg. “Couples who wait until they get the little smiley face or plus sign from their ovulation test may have already missed most of their opportunity to conceive,” she says. Also, if someone is using these kits to avoid pregnancy, the test won’t provide enough advance warning, finds a 2014 study in the Journal of the American Board of Family Medicine.
Another issue is that LH kits do not confirm that ovulation has actually occurred, Leiva says. That matters, because in some cases a woman’s egg may fail to pass into the fallopian tube even though her LH levels have jumped. (He and colleagues are studying a new progesterone urine test that could reveal whether a woman has actually ovulated. But for now, verifying this requires an ultrasound or blood test.)
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LH tests are not a woman’s only option. Newer saliva-based tests employ a mini-microscope to help a woman spot changes in her spit that indicate elevated estrogen levels, a sign that she’s about to ovulate. A 2015 study from European researchers suggests these saliva tests are accurate. But the FDA warns that factors including eating, drinking and brushing your teeth can throw off the results. (On the plus side, the device is reusable, so you don’t have to keep spending money on urine strips.)
Some other methods—including a vaginal ring that predicts ovulation by monitoring your body temperature via smartphone app—may also soon shake up the market. But Flyckt says that, despite their helpfulness, healthy young women probably don’t need to drop $30 or more on a bunch of ovulation test strips or kits. “If a woman has a regular menstrual cycle, which is at or around 28 days, she’ll probably ovulate around day 14, right smack dab in the middle of it,” she says. “So if she begins having intercourse every other day starting around day 10 of her cycle, she’s unlikely to miss her window of fertility.”
On the other hand, for women who have irregular periods, or those who are “new to the whole thing and want some affirmation that everything’s happening normally,” these kits can be helpful and reassuring, she says.
If you fall into either of those camps—or if you just feel better knowing exactly what your body’s up to—Leiva recommends a combination of LH kits and something called cervical mucous monitoring (CMM).
When a woman approaches ovulation, her cervical mucous tends to change from a creamy white or yellowish fluid to a slippery, transparent and elastic fluid similar to raw egg whites, Leiva says. This change in consistency makes it easier for a man’s sperm to reach her egg, he says. By checking the surface of her vulva daily following her period, women can detect this change in mucous consistency, which tends to occur roughly 24 hours before ovulation.
“If you use both methods, there’s a very good chance one or the other will be positive just before ovulation, which can allow intimacy if pregnancy is desired,” he says.
Of course, when and whether a woman ovulates is just one of many things that have to go perfectly for her to conceive. “I have patients who’ve gotten really caught up in the timing and tracking of ovulating and come to me with years of data, but they never thought to have sperm tested or look for something else that may be interfering,” Flyckt says.
For women under 35, she recommends seeing a fertility specialist if a year passes without success. “If over 35, see someone after six months, and right away if you’re over 40,” she says.
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