The term gestational trophoblastic disease (GTD) refers to certain types of tumors that can occur during pregnancy. These tumors begin in the cells that under normal circumstances would develop into the placenta (the organ that develops during pregnancy and provides the growing fetus with oxygen and nutrition), and they cause the placenta to develop abnormally.
All forms of this condition are treatable, and fewer than 20 percent are cancerous. A viable fetus sometimes develops in the course of a pregnancy affected by gestational trophoblastic disease, but not always.
Different Types of Gestational Trophoblastic Disease
There are three forms of GTD:
A hydatidiform mole, also known as a molar pregnancy, occurs when the fertilized egg contains an extra set of the father’s chromosomes. This causes the placental tissue to transform gradually into a mass of cysts.
A molar pregnancy may be partial or complete. A partial mole forms when an egg is fertilized by two sperm cells, or by a single sperm cell with a duplicate set of chromosomes. Because of this extra set of chromosomes, the embryo is malformed and does not survive, and the placenta transforms into molar tissue.
A complete mole occurs when the egg’s chromosomes are dormant, or when the egg has no chromosomes at all. The tissue that develops from this conception never becomes a viable fetus.
Molar pregnancies are often treated with a dilation and curettage (D & C) procedure, the purpose of which is to remove the growing molar tissue.
Choriocarcinoma is a rare and fast-moving cancer that begins in the placenta. It sometimes begins as a molar pregnancy, or it may grow from tissue accidentally left in the uterus after childbirth or a miscarriage. Choriocarcinoma is extremely malignant, but fortunately it arises in only one out of every 40,000 pregnancies.
Without aggressive treatment, choriocarcinoma will spread into the muscle wall around the uterus, and from there it will spread to other parts of the body, including the liver, the lungs, and possibly even the brain.
Placental-site trophoblastic tumors (PSTT) and epithelioid trophoblastic tumors (ETT) comprise a third category of gestational trophoblastic disease. These tumors form at the site where the placenta attaches to the uterine wall.
This rarely occurs during pregnancy; in most cases, these tumors appear months or years after the delivery of a perfectly healthy, normal baby. In some cases they are not diagnosed until they have spread beyond the uterus and into other organs. Symptoms include amenorrhea (the absence of menstrual bleeding) and a kidney condition known as nephrotic syndrome, in which protein leaks into the affected person’s urine, causing swelling of the feet and ankles, weight gain from retention of fluids, and foam in the urine.
Causes of Gestational Trophoblastic Disease
The causes of gestational trophoblastic disease vary, as noted above. A molar pregnancy is caused by an event that affects the chromosomes at the time of conception. A choriocarcinoma tumor may grow from tissue left behind after childbirth or following an incomplete D & C procedure.
Choriocarcinoma can occur after any type of pregnancy-related event—approximately 25 percent of them occur following normal pregnancies. Another 50 percent occur after molar pregnancies, and the remaining 25 percent occur following an abortion or an ectopic pregnancy.
Gestational trophoblastic disease usually occurs in patients under the age of 20 or over the age of 40. A woman who has had a GTD tumor in the past has a slightly greater risk of having another. People who are of Asian, Native American, or African descent are at greater risk for hydatidiform moles (molar pregnancies) and for choriocarcinoma.
Complications of Gestational Trophoblastic Disease
A woman who has had a molar pregnancy may develop complications in future pregnancy, including preeclampsia or anemia, although most women who have had an episode of gestational trophoblastic disease are able to have perfectly healthy pregnancies in the future. Untreated choriocarcinoma, however, can result in death.
How gestational trophoblastic disease is diagnosed depends on which form of gestational trophoblastic disease the patient has. If your doctor suspects GTD, he or she will want to do blood tests, perform ultrasound testing, and possibly complete a CT scan or MRI. A pelvic exam may reveal swelling of the uterus.
Molar pregnancies, as noted above, are most often treated with D & C procedures. More serious types of tumors may require radiation or chemotherapy treatment. If you are diagnosed with one of these types of gestational trophoblastic disease, your physician will determine the best course of action.