Triploidy is a rare chromosomal abnormality in which fetuses are born with an extra set of chromosomes in their cells.
One set of chromosomes has 23 chromosomes. This is called a haploid set. 46 chromosomes, are called a diploid set while 69 chromosomes, are called a triploid set.
Typical cells have 46 chromosomes, with 23 inherited from the mother and 23 inherited from the father. Triploidy occurs when a fetus gets 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. Others are stillborn before reaching full-term. The few infants that do survive to term have multiple severe birth defects. Some common defects include:
- growth retardation
- heart defects
- neural tube defects, such as spina bifida
Infants born with triploidy do not typically survive more than a few days after delivery.
Children born with mosaic triploidy usually survive for many years after birth. Mosaic triploidy occurs when the amount of chromosomes isn’t the same in every cell. Some cells have 46 chromosomes, while others have 69 chromosomes.
Two different kinds of abnormal fertilization can cause triploidy:
- Digynic fertilization, in which the mother provides the extra set of chromosomes. This usually occurs when the mother has two egg cells fertilized by a single sperm.
- Diandric fertilization, in which the father provides the extra set of chromosomes. This usually occurs when the father’s two sperm at one time fertilizes the egg.
Couples who experience one pregnancy with triploidy aren’t at higher risk for it in future pregnancies. Triploidy is also not hereditary.
Pregnant women carrying fetuses with triploid syndrome may have preeclampsia. Symptoms of this condition include:
- albuminuria, or high levels of the protein albumin in the urine
- edema, or swelling
A chromosome analysis (karyotype) test is the only test that can confirm a triploidy diagnosis. This test counts the number of chromosomes in a fetus’s genes to determine the existence of extra chromosomes.
Triploidy cannot be treated or cured. Pregnancies that last until the baby is delivered are rare. If an infant does survive, the baby usually receives palliative care. Medicinal and surgical treatments are not used because of the ultimately lethal nature of the condition.
If doctors discover triploidy while a woman is pregnant, she can terminate the pregnancy or carry it to term or until a spontaneous miscarriage occurs. If she chooses to carry the baby to term, she should be monitored closely for complications caused by triploidy, including:
- preeclampsia, which can be life-threatening
- choriocarcinoma, a type of cancer rarely caused by tissue left over from a partial molar pregnancy
This article originally appeared on Healthline: Medically Reviewed by Euna Chi, MD on October 14, 2016 — Written by Kimberly Holland and Tim Jewell