Hello and welcome to more or less on the BBC World Service, the show that likes to take a

fresh look at the numbers in the news and in life. I'm Charlotte McDonald. This week,

numbers behind, hashtag natural birth control. A number of TikTok videos have been promoting

the use of natural birth control methods over more conventional methods such as the hormonal

contraceptive pill. I'm not comfortable with putting foreign objects in my body or using

artificial hormones. So I use the natural family planning method and it's amazing! Some have even

thrown around some pretty high numbers for how effective it can be. This method is 99.6% effective

in preventing pregnancy when followed perfectly. It's 99% effective when used properly. But what is

natural birth control? Well the idea behind all birth control is not to get pregnant. Most methods

allow you to have sex whenever you want without getting pregnant. But here I'm using the phrase

natural birth control to mean having unprotected sex on the days you're not fertile and avoiding

unprotected sex on the days in the month where sex might lead to pregnancy, which is roughly six days

a month. Of course it's not straightforward working out when a woman's body is fertile.

Looking into this to the show, I've discovered that there are so many different methods and names

that people mention, natural family planning, rhythm method, calendar method, fertility awareness

methods. My name is Rachel Paragolo-Rudia. I am an associate professor of obstetrics and gynecology

at the University of North Carolina in Chapel Hill at North Carolina. I contacted Rachel in the hope

she might be able to explain more. The first thing she told me is that the best term to use is

fertility awareness based methods. So what are they? Fertility awareness based methods are a group

of methods. It's not one method, but they all have in common that they use one or more biomarkers

of fertility that patients track and then use those biomarkers with either a digital algorithm

or a set of rules to determine the days where that person is highly likely to become pregnant if

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