Dr. Beth Taylor

October 21, 2019

As I approach “the change of life” as my mom would call it, I thought I’d start tracking my periods. I started a few months ago and I have to say it's creepy and disappointing when your phone tells you “today it day one.” I’m also pretty sure my phone will start to use this data to send me ads for tampons or anger management classes the week before my period is expected.


Period tracking has been done for a very long time, mostly for women to predict when their period might come, assess their menstrual/hormonal health and get a sense of ovulation timing when trying to conceive.


When I first started practice many women would bring in notebooks with period dates written in columns, or a paper day-timer calendar with a red star marking each day of menstrual bleeding. Nowadays, women show me their phone with the app open to a sophisticated data sheet.


Apps like Flo, Glow, Ovia, Period Tracker, and such are usually free and let you log the days of menstrual flow, amount of flow, timing of intercourse, and make comments on cervical mucus. They all try to tell you when you are ovulating so as to guide when to have intercourse, if you are trying to conceive.


I ask my patients about their periods and if they have done any tests for ovulation (e.g. urine LH test strips, luteal phase progesterone level, basal body temperature). I’ve noticed that the answer is often “yes I am ovulating… the app tells me.” I want to clarify that apps do not tell you if you are ovulating or not. Apps make the assumption that women ovulate 13 or 14 days prior to their period. So, when you enter your period the app subtracts 13-14 calendar days and says that’s when you ovulated. It then predicts, from the menstrual pattern you enter over a few cycles, which day ovulation is occurring.  It really does not know for sure if you are ovulating. To know this you would need to: have a positive LH surge in your uterine, an elevated luteal phase progesterone level in your blood or a basal body temperature that rises 1-2 days after ovulation.


Now, most women who have a period every 25-33 days ARE ovulating at the time the app predicts. If your periods are less than 25 days or more than 33 days it’s quite possible you are not ovulating even though the app says you are.


I suspect most women already know this, but my public service announcement for tonight is to do some other thing beside using an app to confirm ovulation, especially if your period timing is outside the 25-33 day range.


Dr. Beth Taylor MD, FRCSC

Reproductive Endocrinology & Infertility

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