Recent flush of cellphone fertility apps can have their limitations
In years gone by, women would rely on a wall calendar to work out the timing of their menstrual cycles. They would look to physical signs to tell them when they might be ovulating, and therefore when they’d be most likely to fall pregnant.
Lately we’ve seen the surge in phone apps helping women track their cycles to work out the best time to try for a baby. More than 400 fertility apps are available, and 100 million-plus women use them.
The personalisation and convenience of apps makes them empowering and attractive. But they require some caution.
While fertility apps use individualised information to estimate the most fertile period, they are not wholly reliable. And even if an app indicates when a woman is most fertile, it doesn’t mean a pregnancy will follow if a couple has sex then.
A woman’s cycle has three phases: menstrual bleeding, the follicular phase (an egg-containing follicle is growing) and the luteal phase (the two weeks after ovulation before the next period).
It’s been thought the follicular phase varies between women, whereas the luteal phase is relatively constant — generally around 14 days. All phases are thought to amount to a 28-day cycle.
The time of ovulation, at the end of the follicular phase, is marked by the rise in the luteinising hormone. This can be measured by a blood test or urine dipsticks (as in at-home pregnancy tests).
The most fertile days are the three days leading up to and including ovulation. By 12-24 hours after ovulation, a woman is no longer able to conceive in that cycle.
When a woman logs the beginning of her menstrual cycle, fertility apps try to predict when ovulation might occur and recommends the timing of intercourse to optimise the chance of a pregnancy.
Calendar-based apps rely entirely on menstrual cycle length and an assumption ovulation occurs 14 days before the next period.
Many of the more sophisticated apps collect data on basal body temperature, while some also call for a woman to examine her cervical mucus secretions, or include results from at-home test kits.
There may be options to track mood and feelings, diet and exercise, and intercourse.
Australian researchers recently looked at 36 fertility apps most commonly downloaded by Australian women. The research, yet to be published, indicated less than half (42.7 per cent) of the apps predicted the correct ovulation date.
A published study found the calendarbased apps did not correctly determine the ovulation date when the average length of previous cycles was different to the estimated current cycle length. The prediction of fertile days based solely on previous cycle lengths is a clear limitation of such apps.
For apps collecting temperature data, the prediction of highly fertile days was also commonly missed.
It’s likely the apps which request more information will have better accuracy. But their effectiveness also relies on the user entering data correctly and consistently.
Importantly, a recent study looking at more than 600,000 menstrual cycles from 124,648 women tracked by the Natural Cycles app showed the luteal phase is often much longer or shorter than 14 days. This calls into question the basic premise of a standard 28-day cycle.
We have confirmed this using the Flo app, demonstrating differences in cycle length based on body mass index (BMI), age and ethnic background.
In women who had logged at least three cycles on the Flo app (1.5 million women), we found just 16.3 per cent had a median 28-day cycle. A higher percentage of older women (aged 40+) had shorter cycles, and Asian women and women with a very high BMI tended to have longer cycles.
The evidence so far suggests if you’re trying to have a baby, you shouldn’t rely too heavily on an app — particularly if you’re finding it hard to conceive.
Various factors such as diet, exercise, body weight, and ethnicity can play a role in a woman’s menstrual cycle and a couple’s chance of conceiving. While many apps allow users to input this information, changes in body weight, or times of high stress, aren’t allowed for.