Why You’re Wrong About When You Could Get Pregnant

Photographed by Ashley Armitage.
Period trackers are increasingly popular among women who want to monitor their menstrual cycle. Tracker apps help track when you ovulate, your PMS symptoms and when you're most fertile. Some women even use the apps to plan or avoid pregnancies, but how accurate are they and can they ever be a reliable source of information?
A new study published today in the European Journal of Contraception & Reproductive Healthcare has suggested that calendar-based tracking methods are giving women different results as to when they can get pregnant.
The study, commissioned by contraceptive tracking app Natural Cycles, analysed data from over 42,000 women and 282,235 menstrual cycles. The research found significant discrepancies for determining when a woman is fertile when she used the Standard Days Method or the Rhythm Method, compared to the data collected by the app.
The Standard Days Method is a calendar-based method that identifies the fixed fertile window in a woman's cycle (between days eight and 19) and when a couple should avoid sex if they wish to avoid pregnancy. All other days in a woman's cycle are considered non-fertile. The Rhythm Method requires you to track your period for six to 12 months so you try to predict your future ovulation dates.
This new study found that when using an app's algorithm, the probability of receiving a wrong non-fertile day was 69% lower than with the Rhythm Method and 97% with the Standard Days Method.
Obviously, it's important to keep in mind that this study was commissioned by Natural Cycles, but it does highlight that apps could benefit women if they provide more accurate data than traditional tracking methods.
Research cited by Natural Cycles has found that over half of UK women (59%) do or would use a period tracker to plan their pregnancies, jumping to 69% of women aged between 25 and 34. Eighty-one percent of millennials believe they can plan a pregnancy using these methods, which suggests that they have become a reliable tool. But this study has highlighted the need for young women to understand the difference between each period tracker – analogue or digital – and how the results may differ.
Dr Diana Mansour, vice president of the Faculty of Sexual and Reproductive Healthcare for Clinical Quality, told Refinery29 that while the study did show similarities between the fertility awareness methods, they would not be suitable for those not wanting to get pregnant.
She said: "There are many apps which help users plan or prevent a pregnancy and some are more effective than others. The effectiveness of fertility apps is highly dependent on correct usage, and we know that user-dependent methods are less effective than non-user-dependent methods such as intrauterine contraceptives and implants.
"Fertility awareness apps have the potential to broaden contraceptive choice, but are not the method of choice for those where becoming pregnant would be a disaster. Fertility apps could be a suitable contraceptive method for motivated users who understand the commitment involved and the limitations of the method.
"We can conclude from this study that the fertility awareness methods analysed, including the Natural Cycles app, seem to be similar when it comes to predicting women’s fertile window. However, Natural Cycles can be used from cycle one, while with the rhythm and standard days methods women have to wait and use extra protection, such as condoms, for more days.
"The Natural Cycles website advises that with perfect use of the app, one in 100 women will become pregnant in a year, either because the app wrongly categorised a fertile day as a 'green' day or because the additional contraceptive method failed. Perfect use is a challenge, as it requires women to input data on a daily basis and check their temperature on waking."
She added that without an independent review of every app on the market, it wouldn't be advisable to say that one method works better than another. "Without independent evaluation we can’t say if one app is more effective at preventing unplanned pregnancies compared to other apps or contraceptive methods."

More from Sex & Relationships

R29 Original Series