PATHOGENESIS OF FETAL TRIPLOIDY
Most triploid fetuses are lost during the first trimester due to spontaneous
abortion. The fetuses that do survive into the second trimester are usually have
a wide range of anatomic defects of the head, face heart and extremities, as
well as severe asymmetrical growth restriction (1).
A triploid karyotype is present in 90% of cases with partial mole (2-4).
- ± 80% of triploid fertilizations arise from fertilization
of a haploid ovum with either a single sperm that reduplicates or two
sperm (didandry) (3,5).
- ± 20% are thought to be due to a double maternal
contribution (ovum fails to undergo the first or second meiotic division
prior to fertilization - digyny) (3,5).
- A supernumerary paternal
haploid set is imparted to the ovum resulting in 69 chromosomes with three
possible permutations (1):
- XYY (very few of this
karyotype survive to 8 weeks).
Studies suggest that the maternal contribution to the zygote
is essential for normal embryonal growth and development, while the paternal
contribution is essential for proliferation of extraembryonic tissue (6).
Two phenotypes are described (depending on the parental
origin of the extra haploid set) (7,8):
- Type I fetuses
- Well grown.
- Proportionate head
size (symmetrical growth retardation).
- Partial molar changes
in the placenta.
- Elevated beta hCG
- Increased nuchal translucency
- Type II fetuses
- Severe asymmetrical
- No placentomegaly.
- No placental
- <1/3 of second and
third trimester triploidy.
- Decreased levels of
- Normal nuchal
age by dates = 17 wks
ultrasound = 13 wks
age by dates = 16wks
ultrasound = 12 wks
- Growth retarded fetus (18 wks by dates).
- Flexion deformities.
(9) – over 40% of patients are at risk for preeclampsia and a single report of
HELLP syndrome has been described).
- Dishi N, Surti U, Szulman AE.
Morphologic anomalies in triploid liveborn fetuses. Hum Reprod
- Vassilakos P, Riotton G,
Kajii T. Hydatidiform mole: Two entities. A morphologic and cytogenetic
study with some clinical considerations. Am J Obstet Gynecol 1977;127:167-170.
- Szulman AE, Surti U. The
syndromes of hydatidiform mole. I. Cytogenetic and morphologic
correlations. Am J Obstet Gynecol 1978;131:665-671.
- Szulman AE, Surti U. The
syndromes of hydatidiform mole. II. Morphologic evolution of the complete
and partial mole. Am J Obstet Gynecol 1978;132:22-27.
- Lindor NM, Ney JA, Gaffey TA
et.al. A genetic review of complete and partial hydatidiform moles and
nonmolar triploidy. Mayo Clin Proc 1992;67:791-799.
- Surani MAH, Barton SC,
Norris ML. Nuclear transplantation in the mouse: Hereditable differences
between prenatal genomes after activation of the embryonic genome. Cell
- McFadden DE, Kwong LC, Yam
IYL et.al. Prenatal origin of triploidy in human fetuses: Evidence from
genomic imprinting. Hum Genet 1993;92:465-469.
- Janiaux E, Brown R, Rodeck C
et.al. Prenatal diagnosis of triploidy during the second trimester of
pregnancy. Obstet Gynecol 1996;88:983-989.
- Stefos T, Plachouras N, Mari
G et.al. A case of partial mole pregnancy and atypical type I triploidy
associated wth sever HELLP syndrome at 18 weeks of gestation. Ultrasound
Obstet Gynecol 2002;20:403-404.