How Is Gestational Trophoblastic Disease Diagnosed?

Gestational trophoblastic disease (GTD) is most often found either as a result of abnormal signs or symptoms during pregnancy or from the results of certain tests during routine prenatal care. These may lead the doctor to order other tests.

Blood and urine tests

Blood and urine tests can be used to help diagnose GTD.

Human chorionic gonadotropin (HCG)

Trophoblastic cells of both normal placentas and GTD make a hormone called human chorionic gonadotropin or HCG, which is vital in supporting a pregnancy. HCG is released into the blood, and some of it is excreted in the urine. This hormone has 2 chemical components, and the commonly used blood and urine tests measure one of these, called beta-HCG (βHCG).

HCG is normally found only in the blood or urine of pregnant women. In fact, finding HCG in urine is the basis of most pregnancy tests.

A complete mole usually releases more HCG than a normal placenta, so finding higher than expected HCG levels in the blood can be a sign that a complete mole is present.

However, not all women with GTD have HCG levels that are higher than those seen in a normal pregnancy. For example, most women with partial moles, placental site trophoblastic tumors, and epithelioid trophoblastic tumors have normal or only slightly increased HCG levels.

HCG tests can also help tell if GTD may be present after a pregnancy or miscarriage, as the level of HCG should normally fall to an undetectable level soon afterward.

Along with helping to diagnose GTD, blood HCG levels are also very useful in women already known to have GTD. They can be used to:

  • Help estimate the amount of GTD present in a patient's body. Higher levels of HCG might mean that there are more tumor cells in the body.
  • Determine if treatment is working. HCG levels should drop to normal after treatment.
  • Detect GTD that has come back after treatment

It's especially important to monitor HCG levels during treatment and follow-up to make sure the disease is going or has gone away, or has not returned. The HCG test is generally very accurate. In rare cases, patients may have abnormal substances (antibodies) in their blood that interfere with the HCG test. When these patients' blood samples are tested, the HCG levels appear higher than they really are, a situation known as phantom HCG. In some cases, women have been diagnosed with GTD when it is not actually present. A sign of phantom HCG is having high blood levels of HCG, but normal urine levels (because the abnormal antibodies are not present in urine). If doctors notice that the blood (or serum) levels of HCG are high but the urine levels are not, they can order special tests to distinguish between truly elevated HCG levels and phantom HCG.

Other blood tests

Other tests may provide indirect evidence of GTD. For example, red blood cell counts can detect anemia (having too few red blood cells), which can be caused by uterine bleeding. Human placental lactogen (hPL) is a marker that may be used to follow up patients with placental site trophoblastic tumors.

For women diagnosed with GTD, blood tests are often used to watch for side effects from chemotherapy. Blood cell counts are done to watch the health of the bone marrow (where new blood cells are made), and blood chemistry tests can be used to check the condition of the liver and kidneys.

Other lab tests

Examination of the placenta

After a woman gives birth, the placenta is taken to the lab to be examined. Sometimes an unsuspected choriocarcinoma is found.

Tests of spinal fluid

If symptoms suggest GTD might have spread to the brain or spinal cord or if there is a high HCG level but no tumors are seen on any radiology studies, spinal fluid may be checked for signs of tumor spread. This procedure is called a lumbar puncture or spinal tap. For this test, the patient may lie on their side or sit up. The doctor first numbs an area in the lower part of the back over the spine. A small, hollow needle is then placed between the bones of the spine and into the area around the spinal cord and some of the fluid can be collected through the needle.

Imaging tests

Imaging tests use sound waves, x-rays, magnetic fields, or radioactive substances to create pictures of the inside of your body. Imaging tests may be done to help find out whether a tumor is present and to learn how far it may have spread.

Ultrasound (sonogram)

Ultrasound can identify most cases of GTD that are in the uterus, and will likely be one of the first tests done if your doctor suspects there may be a problem.

To diagnose GTD, a different type of ultrasound called transvaginal ultrasonography is most often used. In this procedure, a small transducer is placed into the vagina. This allows for good images of the uterus for women suspected of having GTD during the first trimester of their pregnancy.

What doctors look for: In a normal pregnancy, ultrasound imaging shows a picture of the developing fetus inside the womb.

In a complete molar pregnancy, however, no fetus can be seen on an ultrasound. Instead, the ultrasound detects the large, grape-like swollen villi that are typical of GTD. Rarely, the ultrasound may show a "twin" pregnancy in which one of the twins is a normal fetus and the other is a hydatidiform mole. This occurs less than 1% of the time.

In a partial molar pregnancy, ultrasound can show an abnormally formed placenta. If a fetus is seen, it is often deformed.

Ultrasound can also be used to help find out if a mole is invading local tissues. If blood levels of HCG are still elevated after the mole has been removed, more exams may need to be done.

Chest x-ray

A chest x-ray may be done in cases of persistent GTD to see if it has spread to your lungs, which is very unlikely unless the cancer is far advanced. However, CT scans of the chest are done more often if your doctor suspects spread outside of the uterus. Either test can be done in an outpatient setting.

Computed tomography (CT) scan

The CT scan  may be done to see if GTD has spread outside the uterus, such as the lungs, brain, or liver.

CT scans take longer than regular x-rays. You need to lie still on a table while they are being done. During the test, the table moves in and out of the scanner, a ring-shaped machine that completely surrounds the table. You might feel a bit confined by the ring you have to lie in while the pictures are being taken.

Magnetic resonance imaging (MRI) scan

MRI scans are most helpful in looking at the brain and spinal cord. They are most likely to be used to scan the brain if GTD has already been found to have spread elsewhere, such as to the lungs. Sometimes they are used to look to see if the tumor has grown into the wall of the uterus.

Positron emission tomography (PET) scan

A PET scan is sometimes useful if your doctor thinks the cancer may have spread (or returned after treatment) but doesn't know where. PET scans can be used instead of several different imaging tests because they scan your whole body. Still, these tests are rarely used for GTD.

Some machines are able to perform both a PET and CT scan at the same time (PET/CT scan). This allows the radiologist to compare areas of higher radioactivity on the PET with the appearance of that area on the CT.

Other tests

Doctors can often be fairly certain of a diagnosis of GTD based on symptoms, blood test results, and imaging tests, but the diagnosis is often made after a procedure called a D&C (dilation and curettage) in patients with abnormal bleeding. The cells from the tissue removed during the D&C are viewed under a microscope. The cells from different types of GTD each look different under the microscope. Sometimes complete and partial moles may be hard to tell apart when they are examined under the microscope early in the first trimester. If so, other tests may be needed to distinguish the 2 types of mole. Some tests, called cytogenetics, look at the number and type of chromosomes of the mole. Other tests may look at certain genes that only come from the mother to see if it is a partial mole versus a complete mole. (D&C is described in Surgery for Gestational Trophoblastic Disease.)

The American Cancer Society medical and editorial content team
Our team is made up of doctors and master’s-prepared nurses with deep knowledge of cancer care as well as journalists, editors, and translators with extensive experience in medical writing.

Last Medical Review: November 21, 2017 Last Revised: November 28, 2017

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