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Gestational trophoblastic disease overview
Gestational trophoblastic disease (GTD) includes several rare tumours that occur in the uterus (womb) and start in the cells that form the placenta during pregnancy. Only women develop gestational trophoblastic disease.
Most gestational trophoblastic diseases are benign (non-cancerous), but some are malignant (cancerous). Benign and malignant forms of this disease are also called gestational trophoblastic neoplasia or gestational trophoblastic tumours.
It is estimated that the malignant forms of gestational trophoblastic disease account for less than 1% of all women’s reproductive system cancers.
Anatomy and physiology
The uterus (womb) is the part of the female reproductive system where a baby grows. The female reproductive system consists of internal and external organs, including the vagina, uterus, cervix, ovaries, Fallopian tubes and the parts that make up the vulva. All the internal organs are in the pelvis, which is the part of the body between the hip bones and below the abdomen.
The function of the uterus is to receive a fertilized egg (ovum) and provide a place for an embryo to grow and develop. The uterus protects the embryo (which is called a fetus after about 8 weeks) during pregnancy. It contracts to push the baby out of the body during birth.
Early in pregnancy, the fertilized egg divides and grows to become a mass of cells called a blastocyst. The blastocyst normally implants (attaches) to the wall of the uterus around the 6th day after conception. The blastocyst contains:
- an embryocyst
- The embryocyst is the inner mass of cells that will become the embryo.
- the trophoblast
- The trophoblast is the outer mass of cells.
- It has very small projections (called chorionic villi) that grow into the lining of the uterus.
- The layers of the trophoblast form the tissue that becomes the placenta and the membranes that surround the embryo. The placenta is attached to the lining of the uterus and provides a way for blood, oxygen and nutrients to move from the mother to the developing fetus.
Gestational trophoblastic disease can occur:
- during pregnancy
- after a miscarriage (spontaneous abortion)
- after tubal pregnancy (implantation of the fertilized egg within the Fallopian tube)
- after normal pregnancy
- after surgical removal of a pregnancy (abortion) or the remains of a pregnancy (dilation and curettage or D&C)
In rare cases, a pregnancy does not progress normally and may form a hydatidiform mole (molar pregnancy). These pregnancies can lack an embryo (embryoblast) and have abnormal trophoblast tissue. The body often aborts hydatidiform moles naturally (spontaneous abortion or miscarriage). If they do not abort naturally, they can cause vaginal bleeding. In these cases, women will need a procedure to remove the trophoblast tissue from the uterus. Any trophoblast tissue left behind in the uterus after a hydatidiform mole is lost naturally or removed may develop into gestational trophoblastic disease (GTD).