It really is amazing that, despite the fact that women menstruate pretty much every 28-35 days, we often know little about our fertile days. This is how many unintended pregnancies occur! And for those struggling with conceiving, this may also be why that is not working. Let’s take a look at the menstrual cycle phases.

The first phase is menstruation. Yes, day 1 of your cycle is the first day of full flow menstruation, not the end. Some doctors say to count it only if it starts by noon, others say by midnight is fine. Most women menstruate for 4-7 days, longer may indicate fibroids or endometriosis. Shorter might indicate a thin endometrium, but most doctors don’t place too much emphasis on this. What they are concerned with is regularity—do you get a period every 28-35 days? If shorter, that could be a luteal phase defect, and if longer, then you might not be ovulating monthly.

Starting concurrently with menstruation is the follicular phase. That’s when the follicles that contain eggs begin to grow. More than one follicle will grow every month, and follicles will grow on both ovaries each month—was anybody else taught that only one ovary develops a follicle each month? However, typically, one follicle becomes dominant and grows bigger and releases an egg while the other follicles regress. This phase lasts until about day 14 for a woman with a 28 day cycle. This phase may be longer if your cycle is longer.

The next phase is ovulation. The ovary releases the egg, the fallopian tube sweeps it up and it begins to move down the tube. This is where the sperm meets up with the egg and fertilizes it. Ovulation can be detected by ovulation testing kits, which measure LH (luteinizing hormone) in the urine. This begins to rise to trigger ovulation, and it peaks quickly and drops off again, all usually within 24 hours. A good question that women ask is how do you know if you caught the LH on the way up or the way down? With these kits, you really don’t know. Nor does it really matter. The egg gets released usually within 24-48 hours after you detect the beginning of the surge, so if you’re catching the fall of it, you’re still within the window of fertility. However, since an egg only lives about 24 hours unfertilized, intercourse 4 days after ovulation will not result in conception.

After that phase is the luteal phase where the follicle that released an egg becomes a corpus luteum, which means “yellow body.” The corpus luteum produces progesterone, which is essential to prepare the endometrium for possible implantation. This phase is pretty much the same for all women, regardless of when you ovulate. In other words, this phase is 14 days long for everyone, give or take a day. If you have a long cycle, the additional days are in the follicular phase, not the luteal phase.

Since sperm live 3-7 days in the fallopian tubes depending on what you read, intercourse on the day of ovulation is not required for conception. What is important is timing intercourse just a few days before and during ovulation, not after, if you’re seeking to conceive. And if you’re trying to prevent conception, you will have to use protection or abstain well in advance of your anticipated ovulation, which is tricky if you only use a calendar. If that’s your intention, you need to look into other methods to help you!