One of the biggest bits of research done on cervical fluid and the cervix crypts was done by Prof. Odeblad. His theory was that: “There are different cervical crypt zones, secreting different mucus units with a different molecular architecture, which would combine to form what we know as cervical mucus and would probably have different functions”. 

In 1968 he distinguished between 2 types of mucus:

  • G – High viscosity, stimulated by progesterone, produced in the G crypts; 
  • E – Low viscosity, stimulated by Estrogen, produced in the E crypts. In his further research, he found that E mucus is composed of 3 other types:  S mucus (1977), L mucus (1978) and P mucus (1991).

Dr Odeblad analysed wet and dry cervical mucus specimens to see their cellular components, structural elements and patterns of ferning and crystals. He was able to note when each type of mucus appeared and disappeared in relation to ovulation and its respective hormonal milieu.

He found out that we have 4 types of cervical fluid:

G mucus (Gestogenic):

The G crypts are stimulated by Progesterone to create G mucus. It is only present in the cervical canal during the infertile phases: in the first infertile phase, the level of the Progesterone is low but sufficient to stimulate the G crypts (G-). After ovulation, the Progesterone level is high and stimulates strongly, therefore the G mucus after ovulation is very dense (G+). The 2 types are impermeable due to the mechanical and chemical natural barrier qualities to sperm.

G mucus contains epithelial cells, leucocytes, lymphocytes and immunoglobulin so it provides an excellent defence against infections.

The G crypts are at the lower end of the cervix. The vulva feels dry, no sensation is associated with G mucus and there are no crystallisation patterns.

Interesting facts:  

  1. G mucus has a high viscosity that creates the impermeable plug at the os. During pregnancy, G mucus is present in the form of a mucus plug which for most women remains in place until it passes in early labour and it is called Gp.
  2. IUD strings disrupt the natural G barrier in people with IUDs.

L mucus (Locking in): 

When Estrogen begins to rise, the L crypts begin to produce the L mucus, which is the first Estrogenic type of mucus that is produced. It is more fluid and starts to descend through the vagina to the vulva where it gets mixed with G mucus. 

It is secreted during the whole fertile phase. With a medium viscosity, it is sticky, a bit elastic and it’s either whiteish or translucent and tacky. It attracts malformed sperm cells or those who move slowly due to its ferning patterns with 90-degree branch crystals. The crypts that produce the L mucus are situated in the lower half of the cervix, above the G crypts and its production is stimulated by medium levels of Estrogen. There are +-200 L crypts. 

The downflow is facilitated by the mucolytic activity of P2 which is in its highest levels at the beginning of the fertile phase. 


  1. L mucus is an alkaline type and it neutralizes the acidic vaginal secretion. It provides optimal conditions for sperm to stay alive. 
  2. L mucus has medium viscosity and it filters out malformed sperm. It has a locking-in effect on abnormal sperm (4-20%) that normally accrues in semen. 
  3. It closes the opening of the S crypts once they are all full of sperm. 
  4. It supplies a supportive framework for S mucus swimming lanes. L & S mucus co-operate to bring the sperm to the crypts -see photo. 

S mucus (Sperm conducting/string like):

Hormones that stimulate S mucus are high levels of Estrogen and Noradrenaline levels that are parallel to LH which maintains the S mucus until ovulation.  

Noradrenaline normally produces effects such as increased heart rate, increased blood pressure, widening of pupils, widening of air passages in the lungs and narrowing of blood vessels in non-essential organs. This enables the body to perform well in stressful situations. It is responsible for the fight or flight response.

S mucus is secreted from the S crypts in the upper half of the cervix and appears 1 – 3 days after the L mucus. There are +-100 crypts that secrete the S mucus and those crypts are located close to the L crypts, facilitating a connection between them.

The S mucus is fluid, wet and slippery. It forms swimming lanes in which sperm cells move along the cervical canal very rapidly, reaching the S crypts in the cervix in 3 – 15 min. The S mucus has a clear, stretchy, wet sensation that lubricates and is slippery due to the effect of L, S & P mucus. It nourishes the sperm that can live in this Estrogenic, fertile environment for up to 5 days. 

It has a structure that facilitates the forward movement of sperm cells. It has small, thin needles that the sperm can “join” inside. 

S mucus functions:

  1. Alkalizing the vaginal acidity.
  2. Creates a nourishing environment for the sperm.
  3. Conveys normal sperm to the S crypts.

P mucus (P-peak):

This mucus is present in maximum amounts on the peak day of the cycle. It secretes in the upper part of the cervical canal and is stimulated by Noradrenaline and Estrogen. It contains enzymes that liquefy and dissolve the L&S mucus. It is characterised by a 60-degree branching hexagonal form.

It has several subtypes, but the 2 most important ones are P2/Pa and P6. 

It has 2 functions:

  1. Dissolve mucus.
  2. Has the capacity to conduct sperm cells from the S crypts to the uterine cavity. 

P2/Pa Mucus is secreted in the crypts in the upper half of the cervix and is stimulated by the fall in Estrogen and the presence of Noradrenaline that is in its maximum at the beginning of the fertile phase (4 – 8 days before ovulation). It can liquefy the G & L mucus (due to its mucolytic activity) to facilitate the S mucus flow, which is essential for the sperm to move to the crypts. After the sperm rests in the S crypts, it liquefies the L mucus and frees the sperm to go up.

Pt mucus appears at a woman’s peak day. Less is known about this type, but Odeblad found it to be a very thin variety from the upper half of the cervix.

P6 mucus: secretes in the highest part of the cervical canal, also known as the dome, where there are +-40 crypts. At its junction with the body of the uterus (isthmus), it forms hexagonal “plates” or stars. It appears shortly after ovulation and is influenced by Estrogen and Noradrenaline. Its function is to convey the sperm between its “plates” of mucus to the uterine cavity.

It creates a sensation that is extremely slippery and lubricated. 

Other secretions we have:

Z secretion (enzymes):

It is secreted from the upper part of the cervical crypts, near the uterine isthmus and is present in all the phases of the cycle. It contains many granules which have mucolytic properties and it adheres to the P mucus and forms stellate shapes. 

F mucus (foundation):

It is present during the infertile phase and any physiological function of this type is not known. It contains epithelial cells which come from a fundamental origin. The cells that produce F type are not from the crypts but between the crypts on the inner epithelial wall of the cervix, uterus and the fallopian tubes. It doesn’t change much during the cycle (more in young people). In some cases, it may be the basic infertile pattern.

Vaginal secretion:

As the vaginal epithelial grows, it loses cells and produces small, flaky secretions. It remains at the vulva but is not always noticeable. 

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