Diagnosing gestational trophoblastic disease
Diagnosis is the process of finding the cause of a health problem. The process of diagnosis may seem long and frustrating, but it is important for the doctor to rule out other reasons for a health problem before making a cancer diagnosis. Diagnostic tests for gestational trophoblastic disease (GTD) are usually done when:
- the signs and symptoms of GTD are present
- the doctor suspects GTD after talking with a woman about her health and completing a physical examination
- routine pregnancy tests suggest a problem with the pregnancy
Many of the same tests used to initially diagnose cancer are used to determine the stage (how far the cancer has progressed). Your doctor may also order other tests to check your general health and to help plan your treatment. Tests may include the following.
The medical history is a record of present symptoms, risk factors and all the medical events and problems a person has had in the past. The medical history of a person’s family may also help the doctor to diagnose GTD.
In taking a medical history, the doctor will ask questions about:
- a personal history of
- previous pregnancies, including hydatidiform mole (molar pregnancy) and miscarriage
- previous GTD
- reproductive factors that may increase the risk of GTD
- a family history of GTD
- signs and symptoms that may suggest GTD
A physical examination allows the doctor to look for any signs of GTD. During a physical examination, the doctor may do:
- a pelvic examination to feel the uterus and ovaries
- a vaginal examination to look at the vagina and cervix
- an abdominal examination to feel for lumps or enlargement of organs, such as the liver
Ultrasound uses high-frequency sound waves to make images of structures in the body. A pelvic ultrasound is a routine test done during pregnancy. A routine ultrasound during pregnancy can often detect GTD.
- In women with complete hydatidiform moles, the ultrasound will show that there is no fetus.
- In women with partial moles, the fetus or placenta may not appear normal on ultrasound.
Ultrasound is usually the first test done if the doctor suspects a gestational trophoblastic tumour. It is used to:
- identify most types of gestational trophoblastic disease
- look for spread to other areas of the pelvis or abdomen
- plan treatment
In some cases, an ultrasound probe may be inserted into the vagina (transvaginal ultrasound) to help provide better detail on the ultrasound image.
Tumour markers are substances – usually proteins – in the blood that may indicate the presence of GTD. Tumour marker tests are used to check a person’s response to cancer treatment, but they can also be used to diagnose GTD.
Human chorionic gonadotropin (HCG)
Human chorionic gonadotropin (HCG or b-HCG) is the most common tumour marker test used to diagnose GTD.
- HCG is a hormone that the placenta normally produces during pregnancy. It is the hormone that some pregnancy tests look for. It is not usually found in healthy non-pregnant females.
- HCG is a very sensitive test for diagnosing most gestational trophoblastic tumours. HCG is usually measured in the blood, but it can also be measured in the urine.
- HCG levels are much higher in women with complete hydatidiform moles and gestational choriocarcinoma compared to HCG levels in women with a normal pregnancy.
- With partial moles, the HCG level is higher than normal, but it is not as high as with other types of GTD.
- With placental site tumours, the HCG level may be slightly higher than normal, but it is not considered a good marker for this type of tumour.
- An HCG test can help find GTD after pregnancy or miscarriage as this hormone should not be present in the blood or urine soon afterward.
Human placental lactogen (hPL)
Human placental lactogen (hPL) is a tumour marker that may be used to follow women with placental site trophoblastic tumours.
- hPL is normally produced by the placenta during pregnancy and may be used to see how well the placenta is working in high-risk pregnancies. It is not usually found in non-pregnant females.
- Low hPL levels may indicate that the placenta and fetus are not developing properly.
- High hPL levels are found in women with some types of GTD.
A biopsy is rarely needed to diagnose gestational trophoblastic disease. GTD is often diagnosed after a surgical procedure that removes cells and tissue from the uterus, such as a dilation and curettage (D&C).
Dilation and curettage (D&C)
Dilation and curettage (D&C) is a surgical procedure that uses a small, sharp instrument (curette) to scrape the lining of the uterus. Many women with GTD are diagnosed during a D&C.
- D&C is sometimes done following a miscarriage or normal pregnancy to remove tissues (products of conception) that can sometimes remain in the body.
- D&C is also a treatment option for women with complete or partial hydatidiform moles that are diagnosed by HCG testing or ultrasound.
- D&C will not be done if the doctor suspects a gestational choriocarcinoma because this type of tumour bleeds very easily.
Examination of the placenta
Sometimes the placenta will be sent to the laboratory for examination. Examination of the placenta can help find GTD if a doctor suspects it following an abnormal pregnancy.
Karyotyping is a cytogenetic test (chromosome analysis) that looks for changes to a person’s chromosomes. Karyotyping can find large chromosomal changes like missing or extra chromosomes. Hydatidiform moles (molar pregnancies) result from abnormal fertilization of an egg by 1 or more sperm, which may result in an abnormal number of chromosomes.
Flow cytometry is a laboratory test that is used to sort, count and examine microscopic particles (such as cells or DNA). Cells are measured by staining them with a light-sensitive dye, placing them in fluid and passing them through a laser beam. The laser makes these cells give off a light that is measured and analyzed by a computer. Flow cytometry helps determine the types of cells that are present. It also shows if there are an abnormal number of chromosomes, such as in hydatidiform moles.
Like flow cytometry, immunohistochemistry (or immunocytochemistry) treats a sample of cells with special antibodies. Instead of using a laser and computer, chemicals are added that make the cell change colour if a certain antibody attaches to it. The change in colour can only be seen under a microscope. Immunohistochemistry helps determine the types of cells that are present, which can be helpful in identifying hydatidiform moles.
Blood chemistry tests measure certain chemicals in the blood. They show how well certain organs, like the thyroid, liver and kidneys, are functioning. These tests can also be used to detect abnormalities. They are used to diagnose and stage GTD.
An x-ray uses small doses of radiation to make an image of the body’s structures on film. It is used to look for GTD that may have spread to the lungs.
A CT scan uses special x-ray equipment to make 3-dimensional and cross-sectional images of organs, tissues, bones and blood vessels inside the body. A computer turns the images into detailed pictures. It is used to look for GTD that has spread outside the uterus, such as to the lungs, brain or liver.
Sometimes a contrast medium is used with a CT scan to help provide better detail. It is usually injected into a vein in the hand or arm.
MRI uses powerful magnetic forces and radio-frequency waves to make cross-sectional images of organs, tissues, bones and blood vessels. A computer turns the images into 3-dimensional pictures. It is used to look for GTD that has spread to the brain and spinal cord. It may also help find GTD that has spread into the wall of the uterus.
Sometimes a contrast medium, such as gadolinium, is used with MRI to help provide better detail. It is usually injected into a vein in the hand or arm.
A PET scan uses radioactive materials (radiopharmaceuticals) to detect changes in the metabolic activity of body tissues. A computer analyzes the radioactive patterns and makes 3-dimensional colour images of the area being scanned. It is sometimes used to look for GTD that has:
- spread outside of the uterus
- come back after treatment
Some PET scan machines can perform a CT scan at the same time. This is called PET/CT scanning. A PET/CT scan may sometimes be used to help diagnose or stage GTD.
During a lumbar puncture, the doctor inserts a needle into the spine to collect a small amount of cerebrospinal fluid (CSF) for examination under a microscope. A lumbar puncture may be done to test for HCG to look for GTD that has spread to the brain or spinal cord.
In rare cases, a woman may need a lung biopsy to confirm a diagnosis of GTD that has spread to the lung. A lung biopsy is done by thoracotomy. A thoracotomy is a surgical procedure in which an incision is made through the chest wall to remove lung tissue for examination. This may be necessary if other diagnostic procedures cannot confirm whether or not GTD has spread to the lung.
See deoxyribonucleic acid (DNA).
A type of protein made by the immune system that disarms or destroys a specific foreign substance (antigen) when it appears in the body.
A substance used in some diagnostic procedures to help parts of the body show up better on x-rays or other imaging tests.
In most cases, contrast medium is injected into or around the structure to be examined.
Also called contrast dye or contrast agent.
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