Seemingly Unpredictable: A Lesson in Irregularity

From the first time a young girl gets her period, she’s told how to keep track of it. In school we learn that we should have our periods once a month, or every 4 weeks. In healthcare we learn about a 28 day cycle. This cycle is crucial in fertility. Unfortunately, the typical 28 day cycle is not all that typical. In reality women’s cycles vary in length. And when we break down the cycle, lots of unknowns because known, and questions can be answered.

Today we’ll be focusing on seemingly unpredictable periods. There is not much worse than never knowing when you’re going to have your period. If you don’t have a predictable cycle this can be an ongoing problem for you. While there is variation from cycle to cycle, one thing is consistent. Menses (your period) starts 14 days after ovulation. This is about the same for every healthy woman, no matter how irregular her cycle.

Our cycles are divided into two phases. The follicular phase is the first half (which begins on day 1 of your period), the luteal phase is the second half, and ovulation is what divides the two phases. What varies from person to person (or even from cycle to cycle for some women) is the follicular phase — the phase leading up to ovulation. Textbooks say the follicular phase is 14 days. But your follicular phase can be 10 days or even 25. The second half of your cycle is nearly always 14 days. If you can pinpoint when the follicular phase ends (AKA when ovulation occurs), then you know you will start your period almost exactly 14 days later.

Examples of different cycle lengths. Day 1 is the first day of your period, and beginning of the follicular phase. Notice each luteal phase (second half) is always 14 days.

The most accurate way to pinpoint ovulation is with basal body temperature. If you take your temperature every morning, you will notice a spike immediately after ovulation. This alone is not a good method for birth control, as you only know after ovulation. But once you see the spike, you can put your money on it that you will start your period 2 weeks later. So whether you’re the same every month, get thrown off due to stress, or your cycles vary every single month, you can still get an accurate prediction of when your period will start each cycle. Nice to know eh?