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Just the other day, a friend told me, “I’m pretty sure you have the highest chance of getting pregnant when you’re on your period.”

For the record, that isn’t necessarily true. But I’m not surprised she thought so. There are a lot of myths floating around out there when it comes to women’s health.

As a public health professional, I try to combat these misconceptions whenever I can. For example, on several occasions during my graduate program in maternal and child health, I invited friends and colleagues together for an evening of discussion on fertility awareness. Drawing upon my study of cutting-edge research and ongoing conversations with expert physicians and scientists, I mediated these talks. The results were engaging, fun-filled events in which we chatted about sex, love, and life. We also dispelled quite a few myths.

Some discussions were entertaining, such as what we learned (and didn’t learn) in middle school sex ed. Others were more intimate and included heartfelt admissions of what we wish our partners understood about our sexuality and fertility. Almost all of these conversations highlighted how many misconceptions—and things still to be discovered by science—there are about our fertility.

After laughing, commiserating, and sharing revealing conversations with many women and consulting with experts, here are ten things that I believe every woman deserves to know about her fertility:

01. The average menstrual cycle lasts twenty-eight days, but the majority of menstrual cycles do not.

It’s easy to confuse “average” with “majority.” If the average menstrual cycle length is around twenty-eight days, then that must mean that the majority of menstrual cycles are twenty-eight days, right? Not so.

In a study of more than two thousand menstrual cycles, researchers at the University of Utah Office of Cooperative Reproductive Health found that the 28-day length represents only about 13 percent of cycles. The distribution of cycle length looks like a bell curve, centered around the 28-day mark, which means that there is a lot of variability in average cycle length.

02. Almost all of the variability in menstrual cycle length is due to the pre-ovulation phase of your fertility cycle.

Ovulation is the release of the egg from the ovary. The first part of the cycle (before you ovulate) varies from month to month due to stress, environmental factors, hormonal imbalances, or other causes. The second part of your cycle (after you ovulate until your next period) usually stays relatively stable. If you’re charting your fertility and you notice variability, bring it up with your doctor.

03. Ovulation occurs on day fourteen in less than 10 percent of cycles.

Day one is the first day of your period. Sometimes we assume that ovulation happens on day fourteen of your cycle, right in the middle of that mythical average 28-day cycle. Again, research from the University of Utah shows that, like the length of your entire cycle, there is variability in the day of ovulation.

Why is this important? It’s important for many reasons beyond the scope of this piece, but let’s look at how this affects pregnancy dating, for example. Early pregnancy dating assumes an “average” 28-day cycle and ovulation happening on “average” at day fourteen. Until better dating is achieved through ultrasound later in a pregnancy, or unless you chart using fertility awareness methods and know the exact date of conception, it is likely that this 28-day assumption will throw off the estimated due date of your baby. Maybe only by a few days. Or maybe by a few weeks, which could be the difference between being induced because the doctor thinks you’re at forty-two weeks versus going into labor naturally because you’re actually at forty weeks.

04. You’re more likely to get pregnant if you have sex before (not after) you ovulate.

There is a misconception that once you release an egg (ovulate), you probably will be able to get pregnant any time after that up until your next period, right? Again, not quite.

Conception can only occur on one day. However, intercourse that leads to pregnancy can occur on the day of ovulation and up to several days before ovulation.

Read on to numbers 5 and 6 to find out why.

05. An egg stays alive for twelve to twenty-four hours after ovulation.

After that, the egg dies, and you can no longer conceive until your next cycle.

06. Healthy sperm, on the other hand, can survive anywhere from minutes to days.

Why is that? Why is there so much variation in how long sperm survive? Because how long healthy sperm survives inside of a woman depends on the type of cervical fluid present.

For a few days before you ovulate and on the day of ovulation, you produce a type of cervical fluid that is clear, stretchy, and lubricative because of high estrogen and low progesterone levels. If you look at this type of cervical fluid under a microscope, it appears as beautiful channels in which the sperm can swim and live for several days.

After you ovulate, estrogen levels suddenly drop off, and progesterone levels begin to rise. When this happens, you stop producing this sperm-supporting cervical fluid. Instead, you start producing a type of cervical fluid that literally looks like a stone wall under a microscope. The sperm can’t swim in it, can’t live in it, and die within a few minutes to hours.

Now No. 4 above makes more sense! You release an egg, and, if you had sex even a few days before ovulation, the sperm are alive, happy, healthy, and ready to fertilize the egg right away. So, as long as hormonal levels are within a certain range, and you are producing the clear, stretchy, lubricative fertile cervical fluid that sperm thrive in, you are more likely to get pregnant if you have sex before you ovulate.

07. Just because your temperature changes during your menstrual cycle doesn’t mean you will be able to feel it.

Measuring your basal body temperature is one way of confirming ovulation. Your basal body temperature rises after ovulation and stays elevated until your next period. Some women wonder, though, “If that’s true, why can’t I feel it?”

The temperature rise is only by tenths of a degree Fahrenheit. You need a thermometer that measures temperature to the tenths or even hundredths to see the shift. When you do, it’s a nice confirmation, in addition to other signs of fertility, that ovulation really did happen that cycle.

08. Outside of the fertile window, the probability of pregnancy is very, very low.

Without at least some cervical fluid, it is very unlikely that sperm will survive in the cervix and therefore very unlikely that you will get pregnant. That said, it can be difficult for some women to determine what kind of cervical fluid they’re producing and whether that means they’re about to ovulate because cervical fluid patterns can be quite different for different women. If you want to rely on understanding cervical fluid patterns to achieve or avoid pregnancy, it makes sense to meet with a trained fertility educator.

09. Having irregular cycles does not prevent you from learning more about the signs of your fertility.

Some women may assume that understanding the signs of your fertility is only for women with “regular” cycles or women who are actively trying to get pregnant. As you read in several of the points above, there is natural variability to both cycle length and the fertile window. It is not necessary that you have “regular” cycles in order to learn more about your fertility. In fact, an irregular cycle is all the more cause for paying close attention.

The women I talked to agreed that personalized instruction by well-trained teachers, the motivation to learn, and good communication between partners is essential to get the most out of your fertility awareness.

10. And finally, if you’re feeling like you wish you would have learned some of this information earlier, you’re in good company.

Thousands of women across the country are choosing to learn what they should have learned in those middle school sex ed classes. In recent years, fertility apps such as Glow, Kindara, Ovuline, and others are helping us track the signs of fertility with digital ease.

I hope you enjoyed this abridged version of our evening discussions. Knowledge is power, especially when it comes to your reproductive health.

Authors note: A special thank-you to Joseph B. Stanford, M.D., MSPH, of the University of Utah Office of Cooperative Reproductive Health, who provided consultation on this article.

Photo Credit: Adobe Stock