Ovulation is an important process during the menstrual cycle, which can determine whether you are able to get pregnant, and when. Although many of us learned in health class that unprotected sex at any time could lead to a pregnancy, the window when a woman is fertile each month is relatively small.
People have found ways to predict fertility for centuries. Today, women have many more tools to track ovulation, from urine tests and thermometers to smartphone apps and wearable devices.
It may feel overwhelming when it comes time to track your own ovulation. Whether you're going off birth control and trying to understand your cycle, planning to get pregnant in the future or actively trying, what's the most accurate way to test for ovulation?
TODAY.com spoke with board-certified OB-GYN, endocrinologist and infertility specialist Dr. Lucky Sekhon to find out.
What Happens During Ovulation?
Ovulation occurs when the ovary releases an egg into the fallopian tube, Sekhon tells TODAY.com. At this point, the egg can become fertilized by sperm and lead to a pregnancy.
If a person has a regular 28-day menstrual cycle, this typically happens once a cycle on day 14, Sekhon says.
The menstrual cycle is divided into two parts, with day one being the first day of your flow. During the first two weeks, called the follicular phase, the follicles in the ovaries prepare for ovulation — the hormone progesterone is low, and estrogen is increasing.
Leading up to ovulation, estrogen peaks, triggering a surge in luteinizing hormone (LH), says Sekhon. This signals the ovary to release an egg. In the second half of the cycle after ovulation, the luteal phase, progesterone rises and the lining of the uterus thickens.
When Are You Most Fertile?
During each cycle, there is a finite period called the fertile window, when pregnancy is most likely to occur. "It's typically three to five days leading up to ovulation and the day of ovulation," says Sekhon.
Once an egg is released, it lasts for 12–24 hours. Sperm can survive for three to five days in the reproductive tract, she adds, so it can fertilize an egg after intercourse occurs.
"Ideally, you want the sperm to be sitting in the reproductive tract waiting for the egg," says Sekhon. To maximize the chance of fertilization, it's best have sex during that five-day window, but the peak fertile days are two to three days before ovulation.
After ovulation, the chances of fertilization drop, as the egg is only viable for one day. "It’s not impossible, but concentrating your efforts during that fertile window is most productive,” says Sekhon.
That's why it's crucial to be able to anticipate when ovulation will happen. However, the timing can vary depending on the person. "There's also a lot of confusion about the methods," says Sekhon.
The Most Accurate Way to Test for Ovulation
The most reliable way to predict ovulation is a combination of cycle tracking and other methods to test for fertility indicators.
The simplest tool to calculate your fertile window, called the calendar method, is a great starting point, Sekhon says. This can help you get a sense of your cycle timing, which can inform you when to test for ovulation.
"You can use an app or the old-fashioned method of writing it down in your calendar," says Sekhon. Track the first day of your period, how long it lasts, and the days between each period. Aim to get at least three month's worth of data, she adds.
If you're regular, subtract 14 days from when your next period is due to start. From there, calculate the five-day fertile window before ovulation. "This is the time to be trying," she says.
Everyone's cycle is different. “When people have periods like clockwork, that makes DIY tracking more feasible,” says Sekhon.
However, this method isn't as reliable for people with irregular periods because there isn’t a predictable cycle length to calculate from. These include people with polycystic ovarian syndrome (PCOS), Sekhon notes.
Fortunately, there are other tools to track ovulation that don't rely on a regular cycle.
(If you’re trying to avoid pregnancy, the calendar method is the least effective form of birth control, per the American College of Obstetricians and Gynecologists.)
Ovulation Predictor Kits
"On top of the calendar method, use ovulation predictor kits, which give you real-time data," says Sekhon.
Ovulation predictor kits (OPK) are generally the most accurate way to test for ovulation. These include test strips or digital tests, which detect a rise in luteinizing hormone in urine.
A positive test signals that the ovary is about to release an egg, usually within 24-36 hours, Sekhon says. It's ideal to start testing daily four to five days before ovulation.
She recommends testing early in the afternoon, and waiting at least two hours since the last time you urinated before taking the test. LH is released in bursts, so depending on the time of day you test, it may not be picked up, she adds. Testing more frequently, or every 12 hours, can maximize accuracy.
While OPKs are typically reliable, there is some risk of inaccurate results. PCOS, perimenopause and certain medications can cause LH levels to fluctuate, which may produce a false positive or negative, Sekhon notes. And she cautions that drinking too many liquids can dilute the results.
Cervical Mucus Changes
Another method to predict ovulation is tracking changes in your cervical mucus. "It's less objective, but can be a helpful indicator,” says Sekhon.
During the first half of the cycle, the mucus tends to be thicker. Discharge may look creamy, white or yellow-tinged, per the Cleveland Clinic.
As ovulation approaches, discharge becomes more watery and clear due to the rise in estrogen, Sekhon explains. During the peak fertile window, cervical mucus is very stretchy and slippery, with the consistency of egg whites — this helps transport sperm to the egg. If you notice this, it's a good idea to try to conceive.
After ovulation occurs, the increase in progesterone causes the cervical mucus to become thicker and stickier again, she says.
If you're unsure about assessing your discharge, don't worry. "It can be hard to track. People probably second-guess themselves a lot," says Sekhon.
Basal Body Temperature
Another popular method to track ovulation is measuring your basal body temperature daily throughout your cycle. You can use a regular thermometer or a BBT thermometer, which detects temperature changes to a fraction of a degree.
"Seeing a half a degree Celsius increase in your basal body temperature signals that ovulation has happened," says Sekhon, adding that this is due to the increase in progesterone, which causes a slight rise in body temperature.
However, BBT is a retroactive measure. It only tells you that ovulation has already occurred, rather than predicting your fertility window. “Once your temperature goes up, it’s too late to try,” says Sekhon.
However, BBT tracking can still be useful. "It's another data point to understand (which days) your temperature tends to start rising, which is a marker of ovulation,” Sekhon explains.
Other Signs of Ovulation
“If someone doesn’t have all of those obvious signs, it doesn’t always mean that they’re not ovulating,” says Sekhon.
There are several other common symptoms of ovulation, TODAY.com previously reported.
- Cramping on one side
- Breast tenderness
- Bloating
- Moodiness
- Increased libido
- Spotting
Many of the new wearables and testing devices can track multiple indicators at once, says Sekhon. These include LH, progesterone, estrogen, skin temperature, heart rate and respiration rate.
While some people may find it helpful to have more data, these new tools aren't necessarily more beneficial than existing methods. "I think sometimes it can create more anxiety to have all this information, and it might not be necessary," says Sekhon.
If you have concerns about ovulation or fertility, consult your OB-GYN about additional testing. If you have a partner, consider a semen analysis to determine if there's a male infertility factor.
