If you’re trying to get pregnant, that app on your phone might not be the best for showing your most fertile days.
That’s the conclusion of researchers who tested 33 apps and 20 websites that promised to predict a woman’s fertile time of month. Of the sites and apps tested, only 4 gave the correct information.
"I'd recommend that consumers be cautious, and not completely rely on these sites and apps," said lead researcher Robert Setton, MD. Setton is an ob-gyn resident in New York City.
An online fertility calculator can be helpful for a couple trying to conceive. A woman needs to know the date of her last menstrual period and how long her cycle is, on average. The calculator then tells her which days she has the best chance of conceiving.
Setton and his team decided to test the sites and apps because so many were offered. “To the best of our knowledge, no one has studied their accuracy," he said.
The researchers put the same information into each fertility calculator: the same date for the last menstrual period, and an average menstrual cycle length of 28 days.
According to Setton, research shows that a woman's "fertile window" includes the day she ovulates and the 5 days before that. For a woman with a menstrual cycle of 28 days, that would be days 10 through 15.
Only one website and 3 apps came up with that answer. The rest “were all over the place.” Some gave fertile windows that were 10 days long. Some did not correctly predict the day of ovulation.
The incorrect information could be a problem for couples who are having trouble getting pregnant.
Jennifer Wu, MD, said that women trying to conceive should talk with their healthcare provider about the length of their menstrual cycle and how it changes from month to month. Some women’s cycles can vary from 21 to 35 days. That can throw off a calculator.
In some cases, Wu said, women might get help from an ovulation prediction kit. These are monitors that a woman uses at home. They measure hormone levels in urine or saliva.
Learn more about planning a pregnancy.
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