Uterine Abnormalities: Uterine Septums, Scarring and Structural Causes of Infertility
Uterine abnormalities
are a significant cause of both infertility and recurrent pregnancy
loss. These abnormalities are typically congenital (present from
birth) and are referred to as Mullerian anomalies, as the uterus
develops from a specialized type of tissue called Mullerian tissue.
During embryonic development, a female fetus actually starts out
with two small uteri (plural of uterus) – one near each kidney. As
the fetus develops, each uterus migrates down toward the tissue that
ultimately becomes the vagina, and toward the middle of the
patient’s body where it fuses with the uterus from the other side.
Under normal circumstances, the wall where the two uteri join
reabsorbs completely – from the bottom of the uterus to the top -
resulting in a triangular shaped uterine cavity.
Any alteration of this
development can lead to a Mullerian anomaly. The most common
anomalies include a septate uterus, a bicornuate uterus, a
unicornuate uterus, and a uterine didelphys. A septum occurs when
the two uteri fuse but the wall between them only partially
reabsorbs. The remaining (unreabsorbed) tissue at the top of the
uterus behaves like scar tissue – it has decreased blood flow and
may lack the receptors found in normal uterine lining that are
necessary for implantation to occur. As a result, a successful
pregnancy is much less likely to result. Even if implantation does
occur, but it occurs at the top of the uterus, miscarriage is much
more common.
If the two uteri only
fuse at the very bottom leaving a large unreabsorbed vertical wall
between the two cavities, a bicornuate (Latin for “2 horns”) uterus
results. In this condition, the patient has two small uterine
cavities and a single cervix. These cavities each have an attached
Fallopian tube, so pregnancy is possible, although the chance of
pregnancy in these patients is significantly reduced. In addition,
when pregnancy does result, the risk of premature labor is very
great as the uterus cannot grow as large as it normally would in a
term pregnancy.
Sometimes only one of
the two uteri forms during embryologic development. This uterus has
only one fallopian tube and it is called a unicornuate (Latin for “1
horn”) uterus. Both ovaries will still be present, as they come
from different embryologic tissue. The chance for pregnancy in
these patients is about 60% of that in a patient with a normal
uterus. In addition, pregnancy can only occur during months in
which the woman ovulates from the ovary on the same side as the
fallopian tube (remember there is only one tube present in this
condition).
On very rare occasions,
both uteri are present but they fail to fuse at all. This
condition, called a uterine didelphys, results in two separate uteri
– each with its own fallopian tube and cervix. This condition is
easily recognized by the general gynecologist; as such patients have
two cervices (plural of cervix) on pelvic examination.
With the exception of
the uterine septum, these abnormalities are not repaired because the
chance of improving pregnancy outcome is typically worse following
surgical repair than it is without repair. The situation is vastly
different for the septate uterus, however, as multiple large studies
have shown that surgical repair dramatically improves pregnancy
outcome. Therefore, whenever we diagnose a uterine septum, we will
advocate for hysteroscopic repair - usually under laparoscopic
guidance. This outpatient procedure is designed to resect the septum
so that the entire top of the uterus enlarges, creating a normal
area for implantation to occur. Once this procedure has been
performed, the uterus is much more capable of carrying a pregnancy
to term. In addition, as the repair does not involve making an
incision in the muscular uterine wall, patients who conceive after a
septum resection are not required to have a Cesarean section.
In addition to the
congenital uterine abnormalities described above, there are a
variety of other uterine abnormalities that can develop after
birth. These are referred to as “acquired abnormalities”. Examples
include endometrial polyps, intrauterine adhesions, and uterine
fibroids. These conditions frequently cause symptoms – such as
increasingly severe menstrual cramps, heavier or irregular vaginal
bleeding, or changes in bowel or bladder function. On some
occasions, patients are unaware that they have these conditions and
they are only discovered as part of a fertility evaluation.
Typically large fibroids can be detected during a pelvic
examination, however smaller fibroids, fibroids within the uterine
cavity, polyps, and adhesions can only be detected by some sort of
imaging technique – either a sonogram, an HSG, or a sonohysterogram.
Polyps commonly grow
inside the uterine cavity, originating from the endometrial lining.
These polyps can interfere with implantation, effectively preventing
an embryo from attaching to the uterine wall. It is common for
polyps to induce a chronic inflammatory response within the uterus,
as the body mounts a reaction to try to destroy the polyp. This may
be the mechanism by which polyps interfere with the establishment of
a pregnancy. Polyps can occasionally become malignant, so it is
important to remove them even if you are not interested in
pregnancy.
Intrauterine adhesions
usually from an injury to the uterine cavity. The most common
cause is a D&C performed for a miscarriage. Much less commonly,
adhesions can result from a severe intrauterine infection.
Intrauterine adhesions can be minor, or they can affect the entire
uterine cavity, possibly even leading to complete cessation of
menstrual flow. These severe adhesions are called Asherman’s
syndrome.
Submucosal fibroids
(fibroids located within the uterine cavity) usually cause abnormal
menstrual bleeding. The bleeding can occur at the time of normal
menstrual bleeding or it can occur at other times during the cycle.
It may also be so heavy that it leads to anemia. These benign tumors
require removal even if a patient is not attempting pregnancy. Most
of these fibroids can be removed hysteroscopically if the majority
of the fibroid is within the cavity of the uterus.
Other uterine
abnormalities include fibroids located within the uterine wall
(intramural fibroids), as well as fibroids attached to the outside
of the uterus (subserosal fibroids). The further the fibroid is
away from the endometrial cavity the less it becomes a factor in
regard to fertility and/or carrying a pregnancy. Removal of the
fibroids (myomectomy) is usually the treatment of choice for women
with fibroids who prefer to maintain the ability to become pregnant.
If a uterine fibroid is subserosal, it may be easily removed
laparoscopically. Intramural fibroids may be removed
laparoscopically but in some cases, it may be best to make a little
larger incision just above the pubic bone and remove the fibroids
that way. This procedure, called a laparotomy, is usually performed
if there are many fibroids, if the fibroid(s) are deeply imbedded in
the uterine wall, if the fibroids are very close to the insertion of
the fallopian tube, or if a large fibroid penetrates through the
wall into the uterine cavity. We also perform laparotomies for
fibroids that are too large to safely remove through the
laparoscope.
If a fibroid is removed
from within the wall of the uterus, we will usually advise the
patient that she will require a cesarean section for subsequent
delivery. This is important, as once the uterine wall heals, it is
not as strong as it was before the fibroid (and subsequent surgery
for fibroid removal) affected it.
Another option for
treating fibroids is a procedure called uterine artery embolization
(UAE). During this procedure, performed by an interventional
radiologist, small coils of material are placed into the blood
vessels that feed the fibroids. These coils are delivered through a
catheter inserted through the patient’s groin which can be guided
directly to the fibroid under XRay observation. Studies suggest
that this procedure is very effective in causing shrinkage of large
fibroids as well as a significant reduction in menstrual bleeding,
however many women prefer to have their fibroids removed. In
addition, there is not much data regarding either the effect of this
procedure on subsequent fertility or the safety of labor and
delivery in patients who have undergone UAE. As UAE interferes with
blood flow to the fibroid – and frequently with blood flow to the
surrounding uterine tissue – there is a significant concern that
there may be an adverse effect on subsequent fertility and growth of
a baby. Therefore, most fertility specialists still do not
recommend UAE for women who wish to become pregnant.
