The Mucus Chronicles

It all comes down to mucus. Life. Health. Conception. Contraception…the absence and presence of mucus determines it all.

That’s a heavy statement, I know. But if I could discuss just one topic with anyone curious about their reproductive health and fertility, it would be about mucus. And the most remarkable thing about this, is that many of us were not taught anything about mucus in our sex ed classes. Trust me, I got my Bachelor’s degree in Health Education and there was absolutely no talk of this cyclical “white flow”. It’s a parameter of the menstrual cycle that (optimally) shows up just as frequently as our period, but no one talks about.

So what exactly is cervical mucus and how do we know if we have it?

Cervical mucus is a hydrogel produced by glands in the cervical crypts. (The cervical whattt?) The cervical crypts are ciliated branch-like structures that line the inside of the endocervical canal, which connects the vagina (at the external os) to the uterus (at the internal os). Technically, the cervix is the narrow bottom section of the uterus. The cervical crypts are lined with mucus-producing cells and receptors for both estrogen and progesterone, which are the dominant reproductive hormones. As the follicles (sacks surrounding the immature egg cells) begin to grow at the start of the menstrual cycle, they produce estrogen. As those estrogen levels rise, the cervical crypts begin to produce E-type mucus, or estrogenic mucus. After ovulation, as estrogen levels drop a bit and progesterone levels increase rapidly, the cervical crypts create G-type mucus, or gestagenic mucus.

The estrogenic E-Type mucus is a catch-all term for the various types of estrogenic mucus, including L, S and P-type mucus. Each of these types of mucus have a specific role to play in our fertility. L-mucus is produced at the beginning of the pre-ovulatory follicular phase. It is alkaline (more on that in a moment), helps to dislodge the G-type mucus plug at the beginning of the fertile window, creates a supportive structure for S-mucus to form, filters out defective sperm, and closes the S-crypt openings once they contain several sperm (more on that later). L-mucus on its own is pasty or sticky and can be somewhat elastic, allowing it to stretch just a tiny bit (maybe ¼-¾ of an inch or less). It is often more opaque, but can also be somewhat translucent. S-mucus is secreted from the upper portion of the cervical crypts and is a more fluid-like consistency that tends to be translucent.

S-mucus, when combined with L-mucus, creates hallway like structures within the mucus that helps to activate and guide sperm transport. When you look at estrogenic mucus under a microscope, there seem to be clear channels for the sperm to move through.

The final category of estrogenic mucus is P-type mucus. This mucus has two purposes. It helps to facilitate L-mucus in liquifying the G-type mucus plug at the beginning of the fertile window (opening up the cervix) and it facilitates sperm transport from the cervical crypts towards the uterus and fallopian tubes for potential fertilization in an upward motion at the end of the fertile window. P-mucus is more watery, so when there is a higher ratio of P-mucus, it will feel lubricative when you wipe or touch the mucus, but it will be less viscous and you won’t be able to pick it up off the toilet paper or stretch it between your fingers…it will just look kind of wet on the toilet paper.

All mucus that we can see and feel is fertile.

Let me repeat this. ALL MUCUS IS FERTILE. Now, some Fertility Awareness Methods (like the Justisse Method) categorize the mucus into "Non-Peak" and "Peak" type mucus. However, all cervical mucus is fertile. The Non-Peak and Peak categories just differentiate how estrogenic (or close to ovulation) it might be.

Non-Peak mucus is any mucus that feels dry or smooth when you wipe, is creamy, yellow or white in color, and stretches less than 1 inch.

Peak mucus is any mucus that either feels lubricative when you wipe, has some type of translucent or totally clear color, OR stretches an inch or more.

Sperm can live in both Non-Peak and Peak-type mucus. So if you can feel something slippery when you wipe, or you can see something on the toilet paper (and certainly if you can pick something up off of it), sperm can live there and you’re fertile!

Now, let’s get back to the whole sperm survival and transport thing. Cervical mucus is the medium of life. With the exception of artificial reproductive technologies (ARTs), cervical mucus is the only reason that sperm and eggs ever meet. Generally speaking, the vagina is a fairly acidic environment. And this is great, because we don’t want bacteria living in there. However, sperm are relatively fragile cells that need to be within an alkaline environment to survive.

So the body creates alkaline cervical mucus to temporarily change the pH of the vagina and make it more hospitable for sperm. The mucus also contains sugars and proteins that helps to fuel the mitochondria of the sperm and allow it to live for a few days. When sperm are in contact with E-type mucus they are able to survive within the cervical crypts, uterus and fallopian tubes for about 3-5 days.

We expect people to have mucus present for anywhere from 2-7 days within their cycle. The days that they see this mucus are considered their fertile window. Prior to the beginning of the fertile window (as estrogen levels are still relatively low), and after ovulation (when progesterone is the dominant hormone) G-type mucus creates a mucus plug, which closes up the cervix. What this feels like externally, is a dry sensation when someone wipes before or after going to the bathroom.

When we look at G-type mucus under a microscope it has a web-like structure that makes it impossible for the sperm to penetrate. It’s also more acidic, so the sperm die within minutes of coming into contact with it.