Natural birth control and Fertility Awareness Methods: How effective are they?

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Clue
Dec 14, 2017 · 10 min read
  • Monitoring cervical mucus — cervical mucus changes throughout the menstrual cycle in response to estrogen and progesterone, and usually increases in amount when a person is approaching ovulation or is ovulating. An egg-white-like cervical mucus usually suggests that ovulation will occur soon or has occurred within the last day, whereas thicker, clumpy cervical mucus usually suggests a person has already ovulated.
  • Tracking cycles using a calendar or app
  • Using luteinizing hormone (LH) urine tests — LH spikes within 24 hours before ovulation and this hormone can be detected with at-home urine tests (1–4).
  • Standard Days method — this method is similar to the rhythm method. In short, a person avoids sex or uses a second form of contraception from days 8 to 19 of their cycle (with day 1 being the first day of their period). If your cycles aren’t regular and between 26 and 32 days, this method is not recommended. Five out of 100 people will get pregnant per year if they use this method perfectly, and this method is currently considered a modern contraceptive by the World Health Organization.
  • TwoDay Method — a person who uses this method will check for certain types of cervical mucus every day of their cycle. If yesterday and/or today a person has slippery or egg white cervical mucus, they are potentially fertile and should avoid sex. Four out of 100 people will get pregnant per year if they use this method perfectly.
  • Billings Ovulation Method — Similar to the TwoDay method, the Ovulation method uses cervical mucus to estimate the fertile period. People record descriptions of their cervical mucus onto a chart and follow a set of rules as to when they can have sex. Three out of 100 people will get pregnant per year if they use this method perfectly.
  • Sensiplan (sometimes just called the symptothermal method) — this method uses cervical mucus and BBT readings to determine the fertile window in each individual cycle. Fewer than one out of 100 people will get pregnant per year if they use this method perfectly.
  • Fertility tracking via mobile app — these are relatively new tool that aren’t methods in themselves, but typically use calendar estimates and BBT, and sometimes other symptom inputs, results from luteinizing hormone tests etc. According to recently published research on one such app, one out of 100 people will get pregnant per year if they use this method perfectly; however, these estimates are based off studies with a significant amount of missing data, which may affect this estimate. (6–10)

How effective are FAMs as contraceptives?

Most people don’t use FAMs (or most other forms of birth control) perfectly, and so the effectiveness rate (i.e. what we tend to see in practice) for FAMs is estimated to be lower. How much lower, though, is up for debate. Different FAMs probably have different effectiveness rates, but there are few studies looking at each individual FAM type (ex. Standard Days or TwoDay methods) to know how well the results are generalizable.

Research Factors

Study design can have a strong impact on results. In contraceptive research, it is common to group all types of FAMs together, as far fewer people use FAMs than other forms of contraception or birth control. This is why it is estimated that 1 out of every 4 people who rely on FAMs as a form of contraception will become pregnant in one year (6), as anyone reporting using any FAM is grouped into a single category. This means that someone who doesn’t track their cycles very well and only occasionally abstains from sex is grouped with a person who avoids sex during their entire fertile cycle and is tracking BBT and/or cervical fluid regularly with a well-defined program (like StandardDays or Sensiplan). It’s unlikely that these two people would see the same effectiveness using their respective FAM.

Individuals’ menstrual cycles

Some FAMs, like the Standard Days method, are highly influenced by the regularity of a person’s menstrual cycle. Unfortunately, these methods cannot always accurately predict ovulation before a person enters the fertile window. These forms of FAMs either guess at when a person will enter their fertile window based on past cycles, or tell a person they are in or already past the fertile window.

Measurement accuracy

Combined symptothermal methods have the highest efficacy rates of FAMs for contraception (6, 7). BBT and cervical mucus tracking are cumbersome forms of FAMs, because their use requires daily measurements, usually one or two a day, and highly accurate readings. For example, tracking BBT requires a person to take their temperature immediately upon waking (or after another period of extended rest), and use of the TwoDay method requires checking for cervical mucus at least twice a day (2). If a person does not do this consistently, their recordings and estimates won’t be reliable.

Who might FAMs be a good fit for?

Using certain FAMs can be a lot of work, but some people will consider the work worth it. FAMs have no side effects, are free or inexpensive to use, and can be stopped or started without the help of a healthcare professional. For people who cannot afford, who do not have access to, or are religiously opposed to, or who simply don’t want to use other forms of contraception, using FAMs is an effective alternative (1–3).

FAMs and a second method

FAMs used in conjunction with other forms of contraception, such as condoms or spermicide, can decrease the risk of getting pregnant, especially if a person entirely avoids sex during the potential fertile window and uses another method at every other point (1–3). Using condoms in conjunction with FAMs also reduces the risk of STI transmission.

Why record BBT in Clue?

Clue on its own isn’t recommended for use as a contraceptive. BBT and ovulation tests can be tracked to better improve Clue’s estimates of your cycle length, luteal phase length, fertile window, and ovulation, but this is for informational purposes only and to help you understand how your cycle, body and health.


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Clue helps you understand your cycle so you can discover how to live a full and healthy life.

Clued In

Clued In

Clue helps you understand your cycle so you can discover how to live a full and healthy life. #NowYouKnow