What is a molar pregnancy?
A molar pregnancy is one condition in a range of problems known as
trophoblastic disease, where a pregnancy doesn’t grow as it should. It's
sometimes called a hydatiform mole.
There are two different types of molar pregnancy, which differ in how they form and how they need to be treated.
In
a normal pregnancy, genetic material from the mother and father
combines to form new life. In a molar pregnancy, this process goes
wrong. In a complete molar pregnancy, the maternal chromosomes are lost,
either at conception or while the egg was forming in the ovary, and
only genetic material from the father develops in the cells. In a
partial molar pregnancy, there is a set of maternal chromosomes but also
two sets of chromosomes from the father (ie, double the normal paternal
genetic material).
Complete molar pregnancies develop as a mass
of rapidly growing cells but without a foetus – it cannot therefore
develop into a baby.
In a partial molar pregnancy, a foetus may
start to develop but because of the imbalance in genetic material, it's
always abnormal and can't survive beyond the first three months of
pregnancy.
A molar pregnancy is often harmless, but if untreated
can keep on growing and become invasive, spreading to the organs around
it, or even further afield to the lungs, liver or brain. Very rarely, in
two to three per cent of cases, it may become malignant. These
cancerous types of trophoblastic disease are called choriocarcinoma and
placental site trophoblast tumours.
Symptoms of molar pregnancy
A woman with a hydatidiform mole often feels pregnant and has
symptoms such as morning sickness, probably because the cells of the
molar pregnancy produce the pregnancy hormone hCG (human chorionic
gonadotrophin). This is also the hormone that is used in a pregnancy
test, so she may have a positive result. Some women have no pregnancy
symptoms (as with many normal pregnancies).
As the mole grows
faster than a normal foetus would, the abdomen may become larger more
quickly than would be expected for the dates of the pregnancy. The woman
may experience abdominal pain, and also severe nausea and vomiting
(hyperemesis).
Bleeding from the vagina is another common warning
sign that things are not as they should be. Symptoms similar to
pre-eclampsia - high blood pressure, protein in the urine, swelling of
the feet and legs - may also occur in the first trimester or early in
the second.
Most molar pregnancies are diagnosed at the first
ultrasound scan, which shows a mass of cells without the presence of a
foetus in a complete molar pregnancy or an abnormal non-viable foetus
and placenta in a partial mole.
Causes of molar pregnancy
It remains unclear why a hydatidiform mole develops. However, there
are a number of possible reasons, including defects in the egg, maternal
nutritional deficiencies and uterine abnormalities. Women under 20 or
over 40 are at higher risk.
Having a diet that's low in protein,
folic acid and carotene also increases the risk of a molar pregnancy.
The number of times a women has been pregnant, however, doesn't
influence her risk.
Treatment of molar pregnancy
Once it has been established that a woman is carrying a hydatidiform
mole rather than a healthy foetus, suction evacuation is used to remove
the pregnancy from the womb. This is curative in about four out of five
molar pregnancies.
It's then important to monitor the woman’s
progress and repeatedly measure human chorionic gonadotropin (hCG) to be
sure that everything settles back down to a normal, non-pregnancy
level.
About 15 per cent of women who have had a complete molar
pregnancy and 0.5 per cent of those with a partial molar pregnancy will
require additional treatment, either because hCG levels hit a plateau or
start to rise again, or because of persistent heavy vaginal bleeding.
Further
treatment may involve the use of chemotherapy (usually methotrexate
combined with folinic acid), especially if there's any concern about
invasive or malignant disease.
More than 99 per cent of
hydatidiform moles are cured, and even the more aggressive
choriocarcinoma has a cure rate over 90 per cent.
Subsequent pregnancies
Following successful treatment, most women can have children if
they wish. However, it's strongly recommended that a woman who has had a
molar pregnancy doesn't become pregnant again for 12 months. Although
the likelihood is small, there's a real risk of malignant disease
developing and the increase in pregnancy hormones this would cause can't
be distinguished from those of a real pregnancy. Consequently, good
contraception is required, as is regular monitoring by a hospital
specialist.
READMORE:http://www.bbc.co.uk/health