Fertile Window: Fertility Awareness Methods for Conception and Contraception

In my last blog post, I covered ovulation signs so you can tell whether or not you’re ovulating.

In this post, we’ll utilize some of that information to identify your fertile window.

What’s the fertile window?

The fertile window is the 6(ish) days of your menstrual cycle where pregnancy is possible.

When you ovulate, the egg is only around for a short period of time, i.e., less than 24 hours.

Sperm can survive in the body for up to 5 days.

Using that information, we come up with the approximate length of the fertile window.

Now, how do you apply that to your own cycle? Read on to find out!

What are fertility awareness methods (FAM)?

FAMs are essentially ways to pinpoint your fertile window using the above information, ovulatory signs, and cycle tracking data.

Here are some of the commonly-used FAMs:

  • Basal Body Temperature (BBT): Your body temperature rises after ovulation thanks to progesterone that goes up at this time in the menstrual cycle. The increase is mild: 0.5-1 degrees Fahrenheit or 0.3-0.5 degrees Celsius. You want to take your temperature orally, vaginally, or rectally as soon as you wake up before doing anything (including drinking or eating anything). Take your temperature at around the same time over your whole cycle to get a retrospective on when ovulation happened because your BBT goes up after ovulation. Things like sleep issues, thyroid problems, meds, and other factors can impact your BBT.
  • Cervical Mucus: Egg-whitey and stretchy/stringy mucus can be present starting before ovulation (thanks to estrogen). This can mark the beginning of the fertile window.  After ovulation,  cervical mucus often is tackier and gummier denoting that ovulation has already occurred. Note: not everyone makes a lot of mucus.
  • Ovulation Predictor Kits (OPK) or LH Strips: There are pregnancy test like strips to measure your LH as this hormone surges right before you ovulate. Peak LH happens around 12 hours before the egg is released. Note: conditions like PCOS can lead to LH strips not being an accurate representation of LH because of  baseline elevations in this hormone.
  • Cervical Position: This isn’t a visible sign and definitely requires a bit more involvement, but can be used if you so choose. The cervix (at the bottom of the uterus) becomes shorter and softer mid-cycle. You basically need to insert (clean) fingers into the vaginal tract not only during the fertile window but outside of it as well in order to feel what it’s like and how it changes around ovulation time.
  • Calendar method: this uses cycle tracking data from over six months to mathematically pinpoint the fertile window. To get the first day of the window, subtract 19 from the total number of days in your shortest cycle. To get the last day of the window, you subtract eleven from the longest cycle. For example, if you recorded cycle lengths that varied from 27 to 31 days over a year, then the fertile window is cycle day 8 to 20. There are other  methods like this one out there.
  • Other Signs and Symptoms: Other things can happen at ovulation time because of hormone change. The most common is ovarian pain or mittelschmerz or fluid retention. Some people can get a bit of breakthrough bleeding, which can be associated with an underlying condition

A combination approach of at least two, but ideally more, methods is best. You definitely want long-term data (over 6 months). If your goal is conception, then you can time intercourse appropriately. If your goal is pregnancy prevention, then you can abstain or make sure to use barrier protection during the fertile window (or use emergency contraception in the case of unprotected intercourse or contraceptive failure).

Remember, if you’re using hormonal contraception like the combined oral birth control pill, patch, or Nuvaring, you don’t ovulate so this information doesn’t particularly apply. If you have an implant or hormonal IUD, then you likely ovulate, but sometimes the signs aren’t super clear. If you’re in perimenopause, then the natural hormone change and irregularities can impact the data you gather. These patterns might not be seen in conditions with a high rate of anovulatory cycles (like PCOS and hypothalamic amenorrhea).

This isn’t medical advice so make sure to talk to your healthcare team about your individual health and any questions you may have.

In general, Whether your goal is conception, avoiding pregnancy, or simply understanding your menstrual cycles better, FAMs are a great way to get to know your body!