It is now widely accepted that sperm move from semen into cervical
mucus at their interface as they touch one another during intercourse
(via thrusting) or very shortly thereafter. The older belief that
the cervix dips into the semen collected in the posterior vaginal
vault to allow time for sperm to swim into the mucus is no longer
considered likely. This is important clinically since a retroflexed
and retroverted uterus (often called a "tipped uterus")
has an anteriorly positioned cervix and this had been thought
to be a disadvantage for cervical semen contact. At this time,
the relative position of the uterus in the pelvis and the consequent
position of the cervix in the vagina is not thought to be very
important for fertility.
The pre-ovulatory cervical mucus plays a key role in fertility.
The vaginal vault is normally a hostile environment for sperm.
Sperm is only comfortable in alkaline (basic) solutions such as
semen (with a normal pH of 7.2-7.8). The vaginal vault has a very
low pH (acidic) of about 3-4, and sperm typically will not survive
in the vagina for more than 1-2 hours. The cervical mucus has
a variable pH that depends on the hormonal environment. The hormonal
environment is correlated to the time of the menstrual cycle.
Cervical mucus is alkalinic (basic) just prior to the time of
ovulation when the cervical glands producing the mucus reacts
to the predominance of circulating estrogen to make mucus that
is
- more abundant,
- clearer,
- more elastic (stretchy),
- less cellular,
- more watery (less thick),
- higher in pH, and
- composed of strands that are aligned to allow greater sperm
penetration
If the cervical mucus is "friendly" to sperm then the
sperm should be able to survive in the mucus for at least 2 days.
This preovulatory mucus acts as a kind of reservoir, from which
sperm occasionally move to the fallopian tubes where they normally
fertilize an egg. This has led to the popular recommendation to
have intercourse (relations, sex) every other day in the midcycle.
I have altered the popular "every other day" advise
to recommend daily relations (sex) around the time of ovulation
since sperm counts and quality do not appear to be greatly reduced
with daily ejaculation (at least when there is no apparent male
factor). This seems to provide a greater chance of having fresh
healthy sperm available when an egg is released. With less "friendly"
mucus, the sperm may not last a full 2 days. If say the sperm
only survive for 12 hours then an egg released 13 hours after
intercourse would "wait around" for about a day and
a half before the next sperm were available (on the every other
day intercourse schedule). Since the egg is only fertilizable
for 24 hours (about one day), the egg in this example would not
result in a pregnancy.
Suboptimal mucus conditions that effect sperm survival and penetration
("hostile mucus") include:
* (1) very thick and viscous mucus, which limits sperm
penetration
* (2) antisperm antibodies (in semen or mucus) such that
complement dependent inactivation of sperm within the mucus results
in nonmotile sperm or sperm "wiggling in place" within
2 hours of intercourse
* (3) low (acidic) mucus pH, which may inactivate or destroy
sperm
* (4) infection within the cervix with inflammatory cells
in the mucus digesting the sperm since they are identified as
"foreign material"
Although the importance of the cervical mucus for nourishment
and the survival of the sperm has been recognized for a long time,
there is still no ideal test for mucus quality. The postcoital
test is the most popular test. It involves the couple having relations
(intercourse) at least 2 hours prior to returning to the office
(to allow for complement mediated inactivation of sperm) and in
the office the infertility specialist will check the cervical
mucus for the presence and number of motile sperm. The test should
be completed within 24 hours of intercourse. The World Health
Organization has recommended that one consider performing the
test 6-10 hours following intercourse to further assess longevity
and survival of the sperm.
Despite wide acceptance of the postcoital test, the interpretation
and even the method of performing the test have been highly controversial.
This test was initially proposed by Dr. Simms in the late 1880s
but was not immediately accepted as valuable. Dr. Huhner strongly
supported the postcoital test in the early 1910s. Today, the postcoital
test is frequently referred to as the Simms-Huhner test. Over
the years, the test has undergone considerable modification and
a tremendous effort has focused on cervical mucus research. Yet
even today the medical community does not have a detailed understanding
of the dynamics of cervical mucus as it relates to sperm survival
and fertility.
Biochemical and biophysical changes in the cervical mucus in the
preovulatory time period are understood as enabling sperm to acquire
progressive movement through the cervix so as to gain access to
the upper reproductive tract (including the fallopian tubes).
These changes in the mucus are apparently a result of the influence
of the sex steroids, estrogen and progesterone.
Estrogen generally has a positive effect on cervical mucus with
respect to sperm interaction. The effect of estrogen is countered
(essentially reversed) by the effect of progesterone. Just prior
to the release of the mature egg (ovulation) the estrogen to progesterone
ratio is greatest so that the cervical mucus is optimal for sperm.
Progesterone production rises rapidly with ovulation to disrupt
the beneficial effects of estrogen at the level of the cervical
mucus. The mechanism of the beneficial effect of estrogen is complex,
involving changes in the architectural arrangement of the mycelles
(macromolecular cores that form mucin threads) to create longitudinal
channels (tunnels) within the mucus that allow for progressive
forward movement of sperm through the cervix. Progesterone results
in obliteration of these channels to effectively prevent forward
movement of sperm through the cervix.
The method of performing and interpreting the postcoital test
varies. I have used a number of techniques in the past, with the
most logical to me being the system developed by Dr. Moghessi
(a recent past president of the American Society of Reproductive
Medicine). This is also the system supported by the World Health
Organization (WHO). Essentially, the test provides between 0 and
3 points for each of 5 variables in the evaluation of the mucus
with a total of 10 points being considered normal. The test variables
involve assessment of
- mucus volume (greater volume gives greater points)
- mucus consistency (less viscous gives greater points)
- ferning (greater fern structures give greater points)
- spinnbarkeit (greater stretch or elasticity gives greater
points)
- cellularity (less cells give greater points)
The quality of the cervical mucus is assessed by the score on
these variables. The number of motile sperm and their quality
of movement (rapid linear progressive, sluggish linear or nonlinear,
non progressive, nonmotile) is then assessed. The interpretation
of "how many motile sperm" or "what quality of
movement" is normal is widely debated due to apparent conflicts
within the available literature. These reports include
- (1) greater than 25 progressively motile sperm per microscopic
high power field (400 x magnification) is normal and is also independently
associated with a normal sperm count
- 2) less than 5 motile sperm per high power field indicates
either a decrease in the total motile number of sperm per ejaculate
or abnormal cervical mucus
- (3) no change in pregnancy rates regardless of the number
of sperm identified in the mucus
- (4) 20% of known fertile couples tested had 0-1 motile sperm
per high power field
- (5) 6 of 8 women with abnormal postcoital test results who
then underwent laparoscopy 8-36 hours later had motile sperm found
in the pelvic fluid (that is motile sperm still made it to and
through the fallopian tubes into the fluid behind the uterus)
Abnormal cervical mucus can result from any process that interferes
with the function of cervical glands (mucus is produced by these
glands). This includes surgery to the cervix with destruction
or removal of glands. These surgeries include cryosurgery (freezing),
conization (removal of a cone shaped segment) or LEEP (cauterizing
loop electrode removal of a segment) of the cervix for an abnormal
pap smear.
Treatment of an abnormal postcoital test result is generally placement
of sperm above the cervical mucus within the uterine cavity (intrauterine
insemination). This effectively will bypass the cervical mucus.
A relatively large group of infertility specialists attempt to
correct sperm mucus interaction abnormalities by identifying the
apparent problem. In my experience, these efforts have a low rate
of success (success being a subsequent normal postcoital test
or fertility) and most of my infertility patients are unwilling
to wait for months to diagnose, treat and recheck the cervical
mucus to document an improvement. Specific treatments that can
be considered in an effort to improve poor mucus quality include
(1) viscous thick mucus:
Guiaifenesin by mouth. This is a mucolytic agent that acts to
thin out or lyse mucus. It is the active ingredient in Robitussin
and some other cold medications that act to thin intranasal mucus
(by breaking up the mucus so that it can be expelled)
(2) scanty mucus:
Estrogen preparation by mouth. Premarin in either 0.625 mg or
1.25 mg dosing for 8 to 9 days prior to ovulation may increase
the amount of mucus and possibly its quality. This does not generally
work in the presence of Clomiphene citrate treatment since the
estrogen receptors are blocked.
(3) acidic mucus:
Douching with an alkalinic nontoxic solution such as sodium bicarbonate
(1 tablespoon of baking soda into 1 quart of water) to increase
the pH of the mucus 30 to 60 minutes prior to intercourse. This
has been widely used with mixed success
(4) yellow purulent mucus:
Appropriate antibiotics to treat a presumed or documented infection
should be used.
(5) sperm wiggling in place:
Antisperm antibodies are difficult to effectively treat. Steroids
may inhibit the immune system in general and production of anti
sperm antibodies in particular. These steroids have potentially
serious complications and unclear benefit in this context
(6) use of lubricants:
Discontinuation of lubricants, with the possible exception of
vegetable oil, is recommended while attempting fertility. Most
lubricants including KY jelly and surgilube are toxic to sperm
and can interfere with their survival. Astroglide is a commercially
available synthetic lubricant that is not associated with known
sperm toxicity.
More information on Cervical Mucus Testing is available here.
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