Triploidy is a rare lethal chromosomal (aneupliodic) abnormality caused by the presence of an entire extra chromosomal set.


It is considered the 3 commonest fatal chromosomal anomaly . While it is thought to affect as much as 1-2% of conceptions, the vast majority are thought to undergo spontaneous abortions in the early intrauterine period.



The occurrence of triploidy is considered sporadic. A fetus with triploidy has 69 chromosomes. This can happen in three ways:

  • failure of the division of meiosis I or II in spermatocyte: extra set of paternal chromosomes
  • failure of the division of meiosis I or II in oocyte: extra set of maternal chromosomes
  • dispermy: double fertilisation of the ovum with two sperms

In ~60-75% of cases, the extra set is paternally derived (diandric triploidy). The reported chromosomal compositions are

  • 69XXY: ~60 %
  • 69XXX: ~37%
  • 69XYY: ~3 %

In some cases, there can be diploid/triploid mosaicism.

Serological markers

The serological markers can vary depending on whether the extra set of chromosomes are maternally (digynic) of paternally (diandric) derived.

  • maternal beta HCG and alpha fetoprotein:
    • maternally-derived triploidy: markedly decreased
    • paternally-derived triploidy: markedly increased
  • PAPP-A (pregnancy-associated plasma protein A):
    • maternally-derived triploidy: mildly decreased
    • paternally-derived triploidy: markedly decreased

Radiographic features

Antenatal ultrasound

Sonographic features of pregnancies complicated by fetal triploidy are not uniform and the diagnosis cannot be made by ultrasound alone

However common features include:

Plain radiograph

Not part of routine investigation and most fetuses are not liveborn. Reported features according to one study were :

Treatment and prognosis

Triploidy is incompatible with life and most fetuses miscarriage in the 1trimester. Extremely rare cases with survival few months into postnatal life have been reported . Since most cases are sporadic, the risk of recurrence is, usually, not increased.


Differential diagnosis

Considerations on early ultrasound scans include:

See also

  • partial mole: some consider this term to be synonymous with triploidy