Menstrual cycle apps telling you the day you ovulate, really?

How many of you are using a menstrual cycle or period tracker app? I think in many ways they are a great idea. It makes sense to keep track of when your period might be due. And if you are craving chocolate, feeling bloated or feeling inexplicably angry, knowing that it is probably premenstrual syndrome can be really helpful.

But last year my Masters students alerted me to some frightening information. They said that their period trackers tell them the day they ovulate. If only your cycle dates are being tracked, it is impossible to predict the day of ovulation.

Our text book definition of the menstrual cycle is that we have a 28 day cycle, with ovulation on day 14. And for women with longer or shorter cycles, we used to think that women ovulated 14 days before their next period. So theoretically over time an app could learn about your cycle, and predict which day you might get your period and count back 14 days. But our research shows that the 14 day rule is not accurate.

But guess what – women are individual and this is often not the case. We have recently published an analysis of over 600,000 menstrual cycles in a project I did with the contraception and fertility app Natural Cycles, and we found that only 13% of women had a 28 day cycle and for those with cycles between 25-30 days, they could ovulate anywhere between day 10 and 20. There was a wider range of ovulation days in women with longer cycles.

So it is really important for period tracker apps to stop telling women which day they ovulate. This is just not realistic and can cause serious issues if women think they have ovulated and then have unprotected sex or if they are trying to get pregnant and they are being told the wrong day of ovulation.

I have been told that almost all menstrual cycle apps report the day of ovulation. And for some, you can put in very basic information and they will give you your ovulation days for the whole year. This is so wrong.

The only way to be sure when you ovulate is to measure one of three ovulation markers – your basal body temperature (which is the temperature when you first wake up), your lutenising hormone (which can be done using a test on your urine) or the changes in your cervical mucus. Read more here.

We have just finished a survey of fertility apps – and half of them are only tracking dates, giving women wrong information about their fertile window.

I was at a lecture last week by Sarah Johnson from Clearblue and she reported that many of these apps are giving a very wide fertile window. The Chinese app Meet You (aka Meiyou) has 50 million users, and gives women a 2 week fertile window which is totally incorrect. The fertile window is just 6 days, the day a woman ovulates is the last day of the fertile window as the egg only lasts for 24 hours, but the 5 days before are included as sperm can last for 5 days in the female reproductive tract.  Telling women they are fertile for half of their menstrual cycle is wrong on so many levels.

Does your menstrual cycle app tell you when you are ovulating? What do you think about this?