Research announced today at the 70th AACC Annual Scientific Meeting & Clinical Lab Expo reveals that two out of three of the digital home ovulation tests sold by US retailers do not accurately predict when a woman is ovulating. This information is critical for women trying to get pregnant and could improve their chances by helping them to better select at-home tests to guide intercourse timing.

Women in the US are waiting longer and longer to have their first babies, with the birth rate among women ages 30-34 even surpassing in 2016 that of women 25-29, which was the demographic with the highest birth rate for more than three decades prior. A woman’s fertility declines as she ages, though, dropping from a 20%-25% chance of pregnancy each month in her 20s to 5% by age 40.

As women continue to postpone motherhood, at-home ovulation tests are becoming an increasingly popular way for women to detect when they are ovulating so that they can time intercourse precisely and increase the likelihood of conception in the face of waning fertility. It is therefore imperative that these tests perform with high accuracy, as false results can delay or even prevent conception, which in turn can result in significant emotional stress as well as unnecessary medical investigations into why a couple isn’t conceiving.

A team of researchers led by Sarah Johnson, PhD, of Swiss Precision Diagnostics (SPD) in the UK, however, has found that of the three digital home ovulation tests available in the US in 2017, two of them only detected ovulation to within 1 day in about half of women tested. Only one test gave reliable results, detecting ovulation to within 1 day in about 95% of women tested. Johnson’s team determined this by testing 33 women with three batches of each digital home ovulation test as well as with transvaginal ultrasonography, the gold standard for pinpointing a woman’s day of ovulation. The researchers then compared the at-home test and ultrasonography results.

Notably, all three home tests accurately measure luteinizing hormone (LH) levels, which indicate when a woman is ovulating, but the researchers found that other elements of test design are equally important. Tests should provide enough LH measurement sticks so that women do not run out of test sticks before their day of ovulation—an occurrence that would put an unnecessary burden on women to figure out whether they failed to ovulate or simply need to buy more test sticks. Equally essential is having a reliable digital test reader that not only detects the LH surge that precedes ovulation, but also accurately displays that result.

“In this day and age when women want to get pregnant, planning has become much more important—especially now that women are waiting until later when their fertility may be declining,” said Johnson. “At best, at-home ovulation tests can help women get pregnant quicker. They can also let women know they have detected their most fertile days, so if conception doesn’t occur, they can tell their doctor they’re getting positive home ovulation test results and then the doctor can check other factors that might be preventing conception.”

Disclosure: SPD is the manufacturer of Clearblue, the digital home ovulation test found to have the highest reliability in this study.