Part I of this two article series describes molar pregnancy and the risk it presents. Part II presents one woman’s personal journey upon discovering that she had experienced a partial molar pregnancy.
A molar/partial molar pregnancy is a subject that gets scant attention in pregnancy books, usually a line or two, maybe even a paragraph. Pregnancy books, after all, focus on successful outcomes, and with a molar/partial molar pregnancy, the outcome is miscarriage, also known as spontaneous abortion.
Unlike most other causes of spontaneous abortion, molar/partial molar pregnancy is threatening to the mother. Both conditions are linked with cancer: 20% of women who experience molar pregnancy may develop trophoblastic cancer within the year following the pregnancy, while 5% of women who experience partial molar pregnancy may develop cancer. The cancer is highly treatable, but cancer is something no woman wants to think about when pregnant and looking forward to giving birth. A molar/partial molar pregnancy that is not diagnosed and terminated can lead to death by hemorrhaging.
What Is Molar/Partial Molar Pregnancy?
In a complete molar pregnancy, the ovum has no nucleus. When the sperm fertilizes the empty ovum, no embryo develops. Nor does a placenta develop. Instead, tissue that would have formed a placenta in a normal pregnancy grows into grapelike clusters (called a mole or hydatiform mole) within the uterus.
A partial molar pregnancy results when one of two conditions happen: either two sperm fertilize one ovum or one sperm fertilizes the ovum but its chromosomes are accidentally duplicated. In both instances, there is little chance of a viable embryo developing, though it is possible. If an embryo does grow, it will have two sets of paternal and one set of maternal chromosomes and will likely be severely deformed if more than the normal complement of chromosomes are active. In partial molar pregnancy, there is also molar growth in addition to the embryonic growth.
A rarer situation occurs when a twin pregancy involves one normal embryo and one mole.
In the rare circumstances when a partial molar pregnancy results in a viable embryo or a molar twin pregnancy with one normal embryo happens, medical evidence suggests that the viable embryo will not survive. The mole will grow and spread, destroying the viable embryo.
There is a high risk of maternal hemorrhage in molar and partial molar pregnancies that are not detected and aborted (spontaneously or medically).
When Is Miscarriage Likely to Occur with Molar /Partial Molar Pregnancy?
Most molar and partial molar pregnancies spontaneously abort in the first trimester. The 12 weeks mark is a critical time when the abnormality can be observed on an ultrasound scan. Doctors recommend a dilation and curettage (D & C) when molar or partial molar pregnancies are detected. Because of the cancer risk associated with molar and partial molar pregnancy, a D & C is recommended even if the pregnancy has already spontaneously aborted to ensure that none of the mole remains in the uterus.
Sometimes a molar or partial molar pregnancy is detected because spontaneous abortion has occurred and the patient has had a D & C. The molar or partial molar pregnancy is diagnosed and reported in a pathology report.
What Are the Odds of Having a Molar/ Partial Molar Pregnancy?
Experts disagree as to the odds of a molar or partial molar pregnancy occurring. Some experts state that molar or partial molar pregnancy is a common occurrence and that most such pregnancies spontaneously abort early without detection. Other experts place the odds of a molar pregnancy occurring at somewhere between 1:1000 and 1:1500, with the odds of a second occurrence being higher.
Why Is a Molar/Partial Molar Pregnancy Dangerous to the Mother?
Molar pregnancy is dangerous to the mother for two reasons: trophoblastic cancer and death by hemorrhage.
The products of conception create an ideal growth medium for a normal fetus which will grow faster than at any other time during life. Unfortunately, when a normal fetus does not develop, this medium can be used by another growth such as a tumor. For this reason, trophoblastic cancer can grow quickly if not detected and treated.
Medical experts have stated that there is a 20% risk that a woman who experiences a molar pregnancy will develop cancer within the one year period following the pregnancy. The risk with a partial molar pregnancy is about 5%.
Molar pregnancies that are not aborted, spontaneously or medically, can lead to death by hemorrhage. Fortunately, this is unlikely to happen to women receiving medical care during their pregnancies. If a heart beat is not detectable with a doppler device, a woman will typically undergo a sonogram by 12 weeks, at which time the molar growth is detectable.
In cases of molar/partial molar pregnancy, death by hemorrhage becomes a major risk by about the 20th week post conception.
Scant case histories are available to guide women with partial molar pregnancies attempting to carry a viable fetus to term because viable partial molar pregnancies are such a rare occurrence. The medical literature suggests that attempting to carry a viable fetus in a partial molar pregnancy to term is inadvisable and that successfully doing so is impossible. The overwhelming risk is that both mother and fetus will succumb before the fetus is delivered.
What Is the Protocol Post-Molar Pregnancy?
Women who are known to have experienced a molar or partial molar pregnancy are typically advised not to become pregnant for one year following the pregnancy. In the event trophoblastic cancer does occur, pregnancy is not recommended until one year post treatment.
One reason for this precaution is that the method of testing for trophoblastic cancer is the use of a pregnancy test. If the test indicates pregnancy hormones increasing, cancer is assumed to be present. Pregnancy would render this diagnostic tool useless.
A pregnancy could exacerbate any developing cancer.
Cancer treatment may present risk to the fetus; there is scant evidence available on the effects of chemotherapy during the first trimester of pregnancy; data on fetal risk from maternal chemotherapy is generally derived from breast cancer studies in which chemotherapy differing from the chemotherapy used for trophoblastic cancer was used during the third trimester of pregnancy.
After a molar/partial molar pregnancy, women are advised to have a chest x-ray or MRI to detect any trophoblastic cancer that may have gone undetected and spread to the lungs. The lungs are the first organ to which trophoblastic cancer usually spreads.
The likelihood of a woman experiencing a molar or partial molar pregnancy may be small but it is a subject about which women who are pregnant or thinking of becoming pregnant should become informed.
Note that the author is not a health care professional and is providing general information, not health care advice. Women need to consult a health care provider if they suspect they may be experiencing, or have experienced, a molar/partial molar pregnancy or to obtain medical information about the subject.
