Miscarriage (cont.)
What causes a miscarriage, and what are the tests for the different causes?
The cause of a miscarriage cannot always be determined.
The most common known causes of miscarriage in the first third of pregnancy (1st
trimester) are chromosomal abnormalities, collagen vascular disease (such as
lupus), diabetes, other hormonal problems infection, and congenital (present at
birth) abnormalities of the uterus. Chromosomal abnormalities of the fetus are
the most common cause of early miscarriages, including blighted ovum (see above). Each of
the causes will be described below.
Chromosomes are
microscopic components of every cell in the body that carry all of the genetic
material that determine hair color, eye color, and our
overall appearance and makeup. These chromosomes duplicate themselves and divide
many times during the process of development, and there are numerous points
along the way where a problem can occur. Certain genetic abnormalities are known
to be more prevalent in couples that experience repeated pregnancy losses. These
genetic traits can be screened for by blood tests prior to attempting to become
pregnant. Half of the fetal tissue from1st trimester miscarriages contain
abnormal chromosomes. This number drops to 20% with 2nd trimester miscarriages.
In other words, abnormal chromosomes are more common with 1st trimester than
with 2nd trimester miscarriages. First trimester miscarriages are so very common
that unless they occur more than once, they are not considered "abnormal" per
se. They do not prompt further evaluation unless they occur more than once. In
contrast, 2nd trimester miscarriages are more unusual, and therefore may trigger
evaluation even after a first occurrence. It is therefore clear that causes of
miscarriages seem to vary according to trimester.
Chromosomal abnormalities also become more common with
aging, and women over age 35 have a higher rate of miscarriage than younger
women. Advancing maternal
age is the most significant risk factor for early miscarriage in otherwise
healthy women.
Collagen vascular diseases are illnesses in which a
person's own immune system attacks their own organs. These diseases can be
potentially very serious, either during or between pregnancies. In these
diseases, a woman makes antibodies to her own body's tissues. Examples of
collagen vascular diseases associated with an increased risk of miscarriage are
systemic lupus
erythematosus, and antiphospholipid antibody syndrome. Blood tests can confirm
the presence of abnormal antibodies and are used to diagnose these conditions.
Diabetes generally can be well-managed during pregnancy,
if a woman and her doctor work closely together. However, if the diabetes is
insufficiently controlled, not only is the risk of miscarriages higher, but the
baby can have major birth defects. Other problems can also occur in relation to
diabetes during pregnancy. Good control of blood sugars during pregnancy is very
important.
Hormonal factors may be associated with an increased risk
of miscarriage, including Cushing's Syndrome, thyroid disease, and
polycystic
ovary syndrome. It has also been suggested that inadequate function of the
corpus luteum in the ovary (which produced progesterone necessary for maintenance of the very early
stages of pregnancy) may lead to miscarriage. Termed luteal phase defect, this
is a controversial issue, since several studies have not supported the theory of
luteal phase defect as a cause of pregnancy loss.
Maternal infection with a large number of different organisms has been
associated with an increased risk of miscarriage. Fetal or placental infection by
the offending organism then leads to pregnancy loss. Examples of infections that
have been associated with miscarriage include infections by Listeria
monocytogenes, Toxoplasma gondii, parvovirus B19, rubella, herpes simplex,
cytomegalovirus, and
lymphocytic choriomeningitis virus. Abnormal anatomy of the uterus can also
cause miscarriages. In some women there can be a tissue bridge (uterine septum),
that acts like a partial wall dividing the uterine cavity into sections. The
septum usually has a very poor blood supply, and is not well suited for
placental attachment and growth. Therefore, an embryo implanting on the septum
would be at increased risk of miscarriage.
Other structural abnormalities can result from benign
growths in the uterus called fibroids.
Fibroid tumors (leiomyomata) are benign
growths of muscle cells in the uterus. While most fibroid tumors do not cause
miscarriages, (in fact, they are a rare cause of
infertility), some can
interfere with the embryo implantation and the embryo's blood supply, thereby causing miscarriage.
Invasive surgical procedures in the uterus, such as amniocentesis and
chorionic villus sampling, also slightly increase the risk of miscarriage.
Next: What does NOT cause miscarriage? »
- Dilation and Curettage (D&C) - Read about dilation and Curettage (D&C), a procedure performed for a variety of reasons including determining the cause of abnormal uterine (vaginal) bleeding, tissue removal after miscarriage, or abortion.
- Lupus - Get information on lupus (SLE) disease treatment, signs, diagnosis, types of symptoms (butterfly, discoid rash), causes, pregnancy flares, prevention and statistics.
- Amniocentesis - Learn about amniocentesis, a procedure that examines the chromosomes of the fetus to determine lung maturity, and the possiblities of birth defects.
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