Charting gives us a host of insights into our bodies which non-charting women aren’t privy to – we know when we’re fertile, we know when we’ve ovulated, and we can often predict to the day when our periods will arrive. While knowing in advance when to expect our periods can ensure we’re never caught off-guard without a pad, tampon, or menstrual cup handy, predicting our periods can sometimes be a source of stress – we also know to the day when our periods are late! If you’re trying to avoid pregnancy with FAM, an unexpected extra day at the end of your luteal phase can be a stressful experience. If you’re having a longer luteal phase than you’ve ever had before, it may only seem natural to assume that you’re pregnant. But instead of spending the day stressed out and trotting to the bathroom every half hour to see if your period has started, try to relax. I’m going to allay your fears with data!
A study from the College of Nursing in 2006 monitored 141 healthy, cycling women for 3 to 13 months with an electronic fertility monitor, recording the lengths of the phases of their menstrual cycles, including menses, the follicular phase (the phase before ovulation), fertile phase (the phase with fertile cervical fluid), and luteal phase (the phase after ovulation). The researchers examined the differences in lengths of these phases between women (overall variability of the participants compared to each other), as well as the differences in lengths of these phases within women (variability of each woman’s cycles compared to her other cycles).
The researchers found that, while the luteal phase tends to be the most consistent phase within women, it still contributes a whole 25% of the overall within-woman variability of her cycle lengths. In other words, one-fourth of the variability in women’s cycle lengths may be attributed to inconsistent lengths of the luteal phase – generally, this luteal phase variability is limited to plus or minus a few days, but a whole 9%(!) of the women in this study experienced luteal phase variability greater than 7 days. That’s a lot of variation!
The take-home point to absorb from these findings is that variations in the luteal phase are completely normal, even among healthy cycling women. If you ever find yourself worried because your period is a day or two late, don’t panic. Take a look at your chart and ask yourself the following question: Did you follow the four rules of FAM? If the answer is yes, then take a breath of relief, keep your menstrual supplies handy, and enjoy your bonus day(s) of infertility stress-free. According to a dedicated study on the efficacy of the sympto-thermal method (STM) as birth control, STM is 99.4% effective over 13 cycles when there is no unprotected intercourse in the fertile time. Since you’re only looking at one cycle, your chance of pregnancy for this cycle is .03%. That’s a very small chance – just three percent of a percent! It’s far more likely you’re simply experiencing normal luteal phase variation rather than a pregnancy.
The purpose of this post is to show you that there are alternate explanations for a late period besides pregnancy. Of course, the best way to relax about a late period is to know you've been following the rules! But if you did have intercourse on a fertile day this cycle, it’s still not quite time to panic. Your chances of pregnancy will vary greatly depending on how many days prior to or after your temperature shift you had sex, the qualities of your cervical fluid at the time, and even your age. According to Toni Weschler’s Taking Charge of Your Fertility, you can be confident that you are pregnant on your 18th high-temperature day after ovulation. So if you haven’t reached that 18th day yet, try to relax! Be confident, both in FAM itself and your ability to use it. The data are on your side!