Triploidy is a chromosomal abnormality characterized by the presence of an entire extra set of chromosomes. A normal set of chromosomes, called a haploid set, consists of 23 chromosomes. Human cells have two haploid sets, for a total of 46 chromosomes. This pair of haploid sets is called a diploid set. Triploidy is the presence of a third set, called a triploid set, resulting in a total of 69 chromosomes. Triploidy can be full or mosaic.
Triploidy is a relatively common abnormality, as it is estimated to occur in 1% to 2% of pregnancies; however, the condition has an incredibly high miscarriage rate. It is estimated that for every 1 infant born alive, 1,200 are miscarried in early pregnancy. An estimated 43% of miscarriages due to chromosomal abnormalities are the result of triploidy. Due to this high rate of miscarriage, triploidy has an incidence rate of 1 in 10,000 live births.
Triploidy is associated with anomalies of the head and face such as cleft lip and cleft palate, congenital heart defects such as atrial septal defect (ASD) and ventricular septal defects (VSD), fusion of the fingers, hydrocephalus, intrauterine growth restriction (IUGR), neural tube defects, oligohydramnios, omphalocele, polyhydramnios, pulmonary hypoplasia, and renal anomalies.
Ultrasound and maternal serum screening in the first and second trimester can provide information regarding the risk that the unborn baby has the condition, but they are not diagnostic tests. The only definite diagnostic prenatal tests for triploidy are fetal karyotype tests like an amniocentesis or chorionic villus sampling (CVS). Fetal karyotype testing is recommended if triploidy is suspected, as the condition poses an increased risk to the mother.
Full triploidy is fatal, typically in the perinatal period; however, the longest living infant with triploidy lived for 10.5 months. The recurrence risk for triploidy depends on the underlying cause. Parental genetic testing is recommended prior to subsequent pregnancies.