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Chelsea Victoria/Stocksy United

Cervical mucus can speak volumes about your fertile window. This is particularly true for watery cervical mucus, which often dovetails ovulation and heralds the opening of this window.

Read on to find out more about this type of important fluid.

Cervical mucus is a type of vaginal discharge produced by your cervix and regulated by your hormones estrogen and progesterone. It is composed of:

  • water
  • fat cells (called lipids)
  • proteins (such as mucin, the main part of mucus)
  • salts

It is also comprised of immune system elements such as:

  • antibodies (proteins that help fight infections)
  • immunoglobulins (proteins that act like antibodies)
  • cytokines (proteins that help signal your immune system)

Cervical mucus helps form the first line of defense against foreign and infectious agents looking to enter your genital tract.

It also plays a key role in functions within this tract such as keeping its lining moist and allowing or blocking the passage of:

  • nutrients
  • gases
  • sperm

Mucus tends to be thick and scant at the start of your menstrual cycle. Mucin proteins form a mesh-like structure that serves as a barrier to sperm and other agents.

As estrogen levels rise, water levels also rise while mucin lessens. This relaxes the mucin barrier and makes your cervical mucus increasingly thinner.

These changes peak at ovulation with the watery mucus becoming more copious and resembling raw egg white.

Cervical mucus responds to hormone changes. Mucus thinning is tied to higher estrogen levels and normal fertility whereas thickening brought on by higher progesterone is thought to play a key role in contraception.

Noting changes in mucus that occur over your menstrual cycle may help predict your fertile window.

The window opens 3 to 5 days (sperm lifespan) before ovulation, which just happens to be the number of days sperm can survive after ejaculation.

The ovulation window closes 1 to 2 days, which is the average number of days an oocyte, or immature egg, can survive after being released.

The water content of mucus tends to be thinnest and most profuse during ovulation, as well as just before and after it. You are more likely to get pregnant if you have vaginal sex during this fertile period.

Tracking the amount and quality of your cervical mucus a few times a day for several cycles may help pinpoint your ovulation pattern and your fertile window.

You can simply observe any cervical mucus present outside your vulva, or you can collect mucus with your fingers or a tissue.

Using an app or online tracker may also help you know when this window is most likely to be open. You enter information about your cervical mucus, and the app analyzes the information to help predict your ovulation cycles.

People with normal menses with molimina symptoms (such as tender breasts, bloating, and fatigue) are more likely to ovulate.

In people for whom this is not the case, here are other ways to monitor or predict ovulation:

Basal body temperature (BBT) charting

In a typical menstrual cycle, measuring basal body temperature (BBT) daily may help pinpoint whether ovulation has occurred.

BBT is the lowest natural body temperature charted after a period of rest using a thermometer calibrated to easily read the temperature range.

This is done around the same time each day (usually each morning before rising). A rise in BBT of 0.5°F (0.3°C) can be seen when progesterone rises after ovulation.

A 2017 research review found BBT charting to be a less reliable method of discerning the fertile window than monitoring cervical mucus.

Variations in cycle length are less helpful in pinpointing the fertile window unless they are very long (over 35 days). Also, the temperature rise tied to ovulation often occurs too late to be helpful if you’re trying to conceive.

According to the American College of Obstetricians and Gynecologists, the symptothermal method identifies the fertile window based on changes in BBT and cervical mucus.

Watery cervical mucus cues the start of the fertile phase whereas higher BBT signals the end of it. Although, the symptothermal method may be used for cycles that are:

  • irregular
  • short
  • long

It can be cumbersome and may not have an edge over other methods.

You can use vaginal and underarm sensors to help simplify and improve the process of gauging body temperature.

These at-home sensors record temperature readings thousands of times per day and use this data to help predict ovulation.

Urine tests

At-home urine kits can also detect the rise in your hormone that regulates the release of an egg. This hormone is called luteinizing hormone (LH), and urine tests can measure LH within 12 hours after it appears in your blood.

To observe baseline levels, people start testing their urine with an ovulation predictor kit 1 to 2 days before the expected surge.

Keep in mind that any health concerns that involve high LH levels (such as menopause and polycystic ovary syndrome) can yield false-positive results even when ovulation has not occurred.

Testing for E2 and LH rise at the same time with a digital or electronic monitor may help lower the chance of a false-positive result. These can detect the rise in these hormones in urine to predict ovulation more exactly.

Blood tests

Conducted by a healthcare provider, blood tests can measure the levels of certain hormones made by your body during your cycle. Common blood tests that help predict ovulation include:

  • Estradiol (E2). This form of the hormone estrogen stimulates the growth of your follicle, a fluid-filled structure that contains an egg. It also regulates the output of cervical mucus and prepares your uterine lining to receive a fertilized egg. E2 levels rise quickly just before you ovulate. The test is taken on day 2 or 3 of your menstrual cycle, with day 1 being the first day of your full menstrual flow.
  • Luteinizing hormone (LH). This hormone prompts release of an egg from your follicle. Blood tests can help detect the LH surge, which usually takes place about 36 hours before an egg is released from your follicle into your fallopian tube. Baseline levels can be taken around day 2 or 3 of your cycle, and then midway through (around day 14 to 28) to detect the surge and possible ovulation.
  • Follicle-stimulating hormone (FSH). This hormone stimulates your follicle to grow in your ovaries. FSH often peaks just before ovulation and can be measured on day 2 or 3 of your cycle.
  • Progesterone. This hormone maintains your uterine lining, where a fertilized egg attaches and supports early pregnancy. It is measured 18 to 24 days after menses starts or 7 days before you expect your next menses. Low levels or levels that are not rising likely indicate that a follicle has not ruptured or released an egg.

Pelvic ultrasound

A pelvic ultrasound can help find which large follicles are ready to release an oocyte. Follicles grow until they rupture and release this egg.

A series of ultrasounds may be performed to help detect these follicles. Given its expense, this method is not routinely used to predict ovulation.

Although a transabdominal ultrasound can be performed, people often prefer transvaginal ultrasounds since they do not require a full bladder.

The tampon-like probe used with a vaginal approach also produces better quality, higher resolution images.

The transabdominal approach is typically reserved for young vagina owners, adult vagina owners who are not sexually active, and when a full survey of your pelvis is needed.

The physical and immune system properties of cervical mucus can impact fertility. While its immune aspects can enhance fertility, antisperm antibodies (ASA) can sometimes:

  • interfere with sperm’s trek through your genital tract
  • alter sperm’s ability to penetrate and fertilize an egg
  • affect an embryo before it implants in your uterus

ASA screening is not routinely performed because, though it may affect sperm, ASA seldom causes subfertility or delays conception.

Also, the presence of ASA does not clearly point to infertility since tests may detect ASA in penis and vagina owners who have typical fertility.

Watery cervical mucus keeps sperm safe from acids within your vagina and guards it as it travels through your reproductive tract.

A 2017 research review suggested that having sex when mucus is thin and watery increases the chance of conception.

Along with facilitating the passage of sperm through your cervix, it supports capacitation — when sperm become functionally mature and can penetrate the outer wall of an egg and fertilize it.

Lack of this mucus type may imply cervical factor infertility — a type of infertility that occurs when the mucus lining your cervix is too thick for sperm to travel beyond your cervix.

A vagina owner’s sexual desire tends to increase when estrogen levels are high and ovulation approaches. An increase in watery cervical mucus coincides with these changes.

Alongside other fluids secreted by your vagina when you’re sexually aroused, watery cervical mucus helps lubricate your vagina during intercourse. This can boost your pleasure and comfort.

Watery cervical mucus tends to be clear and thin. It may also have a mild scent.

Yellow, green, or gray mucus that smells foul may point to an infection or other cause such as diet. You may also have:

  • redness or discoloration
  • swelling
  • itching
  • burning

Talk with your doctor or healthcare provider immediately if you notice these changes to your cervical mucus or vaginal area.

Cervical mucus changes in color and quantity during each menstrual cycle stage. Changes after your period tend to occur in sequence, although these can vary based on your individual cycle length and health status:

  • 3 to 4 days of no discharge
  • 3 to 5 days of scant but sticky and cloudy discharge
  • 3 to 4 days of copious, clear, stretchy, wet, and slippery discharge just before, during, and right after ovulation
  • 11 to 14 days of no discharge, at which time menses starts

Mucus features also change with pregnancy:

  • 6 to 12 days after conception, mucus tends to be clear but thick and gummy
  • early in pregnancy, mucus tends to be dry and white to yellow with the amount increasing as pregnancy advances
  • late in pregnancy, mucus is thick and contains bloody streaks known as show — a normal sign that labor has started

Observing your cervical mucus is one way to try to pinpoint ovulation and your most fertile windows.

Since timing is key to getting pregnant, these tried-and-true methods, along with newer but more precise methods, may help.

To use cervical mucus as a guide, check for thinner, watery cervical mucus.

Increased amounts of thin, clear, and wet, and slippery discharge often occur in the middle of your menstrual cycle and may help you know the best time to have sex if you’re trying to conceive.