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How Cervical Fluid Helps You Get Pregnant (Or Not)

wrote this on December 5, 2014

I recently taught a puberty education course and was approached at the very end by a few curious students.

“I heard you can get pregnant if a boy touches you, because he might have SPERM on his hand!”

“Well, I heard that swallowing sperm can make you pregnant!”

From a young age, we’re led to believe that we can get pregnant any time we even think about having sex. Unfortunately, a lot of this misinformation persists into adulthood (though maybe not to the same degree).

It’s not until they’re actually trying to get pregnant that many women realize it’s not quite so simple. Getting pregnant—or preventing pregnancy, depending on your family planning goals—can feel incredibly daunting. So…what’s the big secret?

While there are many subtle physiological mechanisms that ultimately lead to a pregnancy, there is one (aside from actually ovulating) that is by far the most important: the production of an awesome substance called cervical fluid. There are several reasons why cervical fluid is incredibly vital to getting pregnant (or avoiding it).

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Semen is alkaline.

The makeup of seminal fluid serves a very specific and important purpose in reproduction: ensuring sperm stay alive long enough to fertilize an egg. The pH of seminal fluid ranges anywhere from about 7.2–8.0, making it alkaline.

The vagina is acidic.

The natural pH of the vagina is in the ballpark of 3.8–4.0, making it relatively acidic. Acidic vagina + alkaline semen = dead sperm! But, seriously…sperm die extremely quickly when exposed to the acidity of the vagina. If that’s the case, then why on earth is the vagina so acidic?!

Acidic environments hinder the growth of harmful bacteria, which is why compounds like lactic acid are often added to food as a preservative. In the case of the vagina, its acidity ensures the proper balance of bacterial flora, preventing overgrowth of bad bacteria that can cause issues like vaginal infections. So the pH of your vagina basically helps it keep itself healthy. It just happens to have the side effect of killing sperm.

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Cervical fluid helps sperm stay alive.

Cervical fluid—which is secreted by the cervix in response to estrogen that’s produced by maturing egg follicles—helps to bridge this pH gap so that sperm can reach the egg. As egg follicles mature and prepare for ovulation, cervical fluid becomes increasingly wet and slippery, and its pH rises.

The pH of cervical fluid in the days just before ovulation creates a sperm-friendly environment, protecting them from the low, hostile pH of the vagina. It also helps to weed out any bad or malformed sperm.

Cervical fluid helps you get pregnant (or not).

Since slippery cervical fluid is only produced during certain parts of the menstrual cycle, sperm have a limited opportunity to fertilize an egg. This means if you’re trying to get pregnant, paying attention to your cervical fluid pattern will help you figure out the best days to get busy! Even if you never notice wet, slippery cervical fluid—which is the case for some women—timing sex for the days when your cervical fluid is the most wet will improve your chances of conceiving.

Keeping up with changes in your fluid can also help you avoid pregnancy. Learning about your unique cervical fluid pattern will help you determine which days of your cycle sperm will and won’t be able to survive inside your vagina.

Combining observations of your cervical fluid changes with daily measurements of your basal body temperature—which is your waking temperature—comprises a method called the sympto-thermal method of fertility awareness. The sympto-thermal method is up to 99.6% effective at preventing pregnancy when practiced perfectly. This method also helps maximize your chances of getting pregnant by helping you pinpoint the most fertile days of your cycle. You can learn to practice the sympto-thermal method right from our website.

Jennifer Aldoretta is the cofounder and CEO of Groove. She is an entrepreneur, engineer, and biohacker who is obsessed with periods, nutrition, hormones, and the microbiome.