Triploidy is a rare chromosomal abnormality. Fetuses with Triploidy, or Triploid Syndrome, have an extra set of chromosomes in their cells.
One set of chromosomes has 23 chromosomes and is called a haploid set. Two sets, or 46 chromosomes, are called a diploid set. Three sets, or 69 chromosomes, are called a triploid set.
Typical cells have 46 chromosomes, 23 inherited from the mother and 23 inherited from the father. Fetuses with Triploidy inherit an extra set of chromosomes from one of the parents.
Triploidy is a lethal condition. Fetuses with the abnormality rarely survive to birth. Many are spontaneously miscarried during the first trimester or stillborn before reaching full-term. The few infants that do survive to term will have severe and multiple birth defects. These might include growth retardation, heart defects, and neural tube defects (Spina bifida). Infants born with Triploidy typically will not live more than a few days after delivery.
Triploidy is the result of an extra set of chromosomes. This can be the result of two sperm fertilizing one normal egg. It can also occur if a normal sperm fertilizes an egg that has an extra set of chromosomes.
Triploidy occurs in one to two percent of all conceptions. There are no risk factors. Triploidy is not more common in older mothers, like some chromosome abnormalities, such as Down’s syndrome. Couples who have one pregnancy with Triploidy do not have an increased risk in future pregnancies. Triploidy is also not hereditary.
Pregnant women carrying fetuses with Triploid Syndrome may experience preeclampsia. Symptoms of this condition include:
- albuminuria (high levels of albumin, a protein, in the urine)
- edema (swelling)
- hypertension (high blood pressure)
The physical effects of Triploidy in a fetus depend on whether the extra set of chromosomes came from the father or the mother. Maternally inherited chromosomes can cause small heads and a placenta that is enlarged and filled with cysts. Paternally inherited chromosomes can cause severe growth problems, an enlarged head, and a small placenta that does not have cysts.
Infants with Triploidy who reach the full-term stage and are delivered often have one or more of these birth defects:
- abdominal wall defects, such as a hole that causes the intestines to be located outside the body
- abnormal genitalia (in boys)
- cleft lip and cleft palate
- heart defects
- limb abnormalities, such as webbing of the fingers and toes
- kidney defects, such as cystic kidney
- neural tube defects, such as Spina bifida
- wide-set eyes
The only test that can confirm a suspected Triploidy diagnosis is a chromosome analysis (karyotype). This test counts the number of chromosomes present in a fetus’s genes. To perform this test, a doctor will need to obtain a tissue sample from the fetus. Because the fetus and placenta came from the same fertilized egg, a doctor can use a sample of the placenta for testing. Additionally, an amniocentesis can be used to diagnose Triploidy. The doctor extracts amniotic fluid. The sample will then be analyzed for signs of abnormal chromosomes.
Triploidy can be discovered prenatally, before the baby is born. The abnormality may be found if a maternal serum screening test is ordered. This blood test, which is typically performed during the second trimester of pregnancy, is not designed to detect the condition. But it may alert an obstetrician to a potential problem because of other unusual results within the test. Specifically, too much or too little of certain proteins in the blood may signal an abnormal pregnancy. If a serum screening test is problematic, additional tests may be needed.
Triploidy can also be discovered during a sonogram or ultrasound. This imaging test is commonly done during pregnancy to examine the fetus.
Triploidy cannot be treated or cured. Pregnancies that last until the baby is delivered are rare. In the event an infant does survive, doctors and healthcare providers usually provide palliative care. Medicinal and surgical treatments are not used due to the ultimate lethal nature of the condition.
If doctors discover Triploidy while a woman remains pregnant, she has the option to terminate the pregnancy or carry it to term or until a spontaneous miscarriage occurs. If she elects to carry the baby to term, she should be monitored closely for complications caused by Triploidy. These can include pre-eclampsia.