Checking Your BBT Versus Using An OPK — Which Is More Accurate?

When you are trying to conceive, the number of options available for tracking ovulation can feel overwhelming. Between testing and charting and evaluating, um, mucus, it can be hard to choose what will work best for you. Testing your basal body temperature (BBT) and using an ovulation prediction kit (OPK) are two popular methods, but is your BBT more accurate than an OPK? Both are really beneficial at figuring out your most fertile days.

“The key benefit of BBT is it only requires the one time purchase of a good thermometer,” Dr. Janet Choi, a reproductive endocrinologist and the medical director with the Colorado Center for Reproductive Medicine in New York, tells Romper in an email interview. “The problem with BBT is that once the temperature spikes, it's too late that month to try and conceive (as the temperature increases only a day or two after ovulation and, by then, the egg is well and gone)." Therefore, Choi explains, BBT is most useful for women with very predictable menstrual cycles and for women who “don't mind the tedium of monitoring daily temperatures for a week or two at a time each month until they can chart a regular pattern.”

On the other hand, Choi says OPKs are useful at figuring out when ovulation is going to occur. “So if you're having difficulty timing intercourse, an OPK may be helpful,” she says. “I counsel women to have intercourse starting a couple of days before the anticipated LH surge and then once or twice after the kit detects a LH surge (and you can stop checking the OPK once you see a surge). Choi says there are a few downsides to using these kits, including the fact that women can still miss an LH surge (either because they forget to check on that crucial day when the surge is happening or because the urine is so dilute that the strips can't detect the LH rise), as well as the expense of buying and using the kits.

So what exactly is required with each method?

According to Baby Center, BBT is simply your morning body temperature before you do absolutely anything — eating, drinking, moving, and so forth. Think of it as your baseline temperature. Choi says BBT charting requires daily temperature monitoring (typically, first thing in the morning) while using a thermometer that can measure to the tenth of a degree. “Progesterone — the hormone your ovaries make after ovulation — causes the body's temp to increase by a few tenths of a degree,” she says. When using BBT to try and conceive, Choi says the key is to make sure to have sex starting several days before the anticipated temperature rise.

On the other hand, Choi says, OPKs test for the spike in luteinizing hormone (LH) that precedes ovulation by a day or two. “Some of the fancier/higher tech ovulation prediction kits monitor urine estrogen as well because the maturing egg leads to several days of elevated estrogen before the LH spike and ovulation,” she says.

Choi stresses that whether you choose BBT or OPK, either method is best for women with more regular monthly cycles. For women who have polycystic ovarian syndrome or other conditions which can lead to irregular menstrual cycles, ovulation can be very tricky to detect month to month. “In these instances, I advise couples to make sure they're having sex at least two to three times a week in case ovulation happens on an unpredictable day,” she says. “Because while the egg is only usable for 12 to 24 hours after ovulation, sperm can survive and fertilize an egg for up to three to five days after intercourse.”

As always, check with your healthcare provider if you are trying to get pregnant and have questions. Because whether you use OPK, BBT, or you simply DTD, there is a TTC acronym that will lead you to the one you’ve been waiting for — PG.

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