Contraception can be a pain. From the long list of side-effects associated with hormonal pills, to the painful and invasive nature of implants and IUDs, women put up with a lot to avoid getting pregnant. And with the search for a male contraceptive pill that lacks undesirable side-effects (the type that women have put up with for decades) still unfruitful, things look set to stay this way for a while.
Or do they? As the first and only app to become certified as a contraceptive in Europe, Natural Cycles promises a hormone-free, non-invasive alternative to traditional forms of birth control.
Natural Cycles was developed by physicist Dr Elina Berglund, who works at CERN and was part of the team responsible for confirming the existence of the Higgs boson. The app started out as an algorithm Berglund developed after deciding to stop taking hormonal contraceptives. She started looking into the biology of the menstrual cycle and found that ovulation can be accurately predicted by small changes in body temperature, and this data can be used to calculate when an individual is and is not fertile. Berglund began to monitor her own cycle using the algorithm, along with some of her colleagues at CERN. This ended up working so well that her Berglund and her husband decided to develop the algorithm into an app, so that more people could benefit from it. The latest study shows that the app is 99% effective when used perfectly, or 93% effective with typical use (for comparison, the pill is 91% effective with typical use).
So how does a simple fertility awareness method manage to have such success in preventing pregnancy? To answer this, we first need to understand a bit of the biology of the menstrual cycle.
Photo source: https://www.naturalcycles.com/en/science/menstrual-cycle
The menstrual cycle can be roughly divided into three stages: the follicular (pre-ovulatory) phase, ovulation, and the luteal (post-ovulatory) phase. The levels of the hormones oestrogen, progesterone and LH vary over these stages, as shown in the diagram above, with the body’s basal body temperature (temperature at rest) changing as a result of these different levels. This is how Natural Cycles detects where the user is in their menstrual cycle: a temperature taken each morning with a two decimal place thermometer.
During the follicular phase oestrogen levels are high, and progesterone levels low, leading to a lower body temperature. At the end of the follicular phase is the fertile window. This is approximately six days long – starting five days before ovulation occurs. This is because sperm can survive in the uterus and fallopian tubes for up to five days waiting for an egg to fertilise.
At ovulation an egg is released by one of the ovaries, and travels through the fallopian tube, where it can be fertilised if it encounters a sperm (which could have been hanging around in the tube for several days).
After ovulation the luteal phase starts. Progesterone levels increase in order to aid the foetus’s development if fertilisation has occurred. The rise in progesterone causes the basal body temperature to go up an average of 0.3°C. If fertilisation has not occurred the progesterone levels then fall again, and the uterine wall begins to shed with the beginning of menstruation, which starts a new cycle.
From this we can see that there is actually only a window of around 6 days each cycle where fertilisation could actually occur, on all the other days of the cycle intercourse will not result in a pregnancy. The Natural Cycles app uses this logic to assign ‘red’ and ‘green’ days – those on which you do and do not need to use protection, respectively. Of course an app that accurately tracks fertility can also be used to increase chances of pregnancy, and around 20% of Natural Cycles users are in fact using it to aid in becoming pregnant.
However, the app may not be for everyone. Success depends on users strictly abstaining or using barrier protection such as condoms on red days, and making sure to take their temperature each morning, having had a decent amount of sleep (as sleep deprivation can cause fluctuations in the basal body temperature). Those who have irregular menstrual cycles, such as people with PCOS (polycystic ovarian syndrome), which affects around 10% of women, may not benefit so much from Natural Cycles, as the algorithm is likely to give them many more red days per cycle. A subscription to the app also costs around £40 per year, which is pretty pricey considering that all other birth control is free on the NHS (although you do get a thermometer thrown in). Whether that is value for money for a side-effect-free form of contraception is down to the individual.