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CAR: Anomalies - Chromosome

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    Triple X
    YY syndrome


Introduction Antenatal Postnatal West Midlands Data


Polyploidy is caused by one or more complete (haploid) sets of extra chromosomes. Triploidy (3n) is caused by one extra set of chromosomes, mostly 69XXY and tetraploidy (4n) by two extras sets, e.g. 92XXXX. Many affected pregnancies are lost spontaneously as miscarriages and polyploidy occurs in 20% of all chromosomally abnormal spontaneous abortions.

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The clinical expression of polyploidy depends on the source of the additional haploid set of chromosomes. If the extra set is paternally derived (diandry) the fetus has a large head and small body (i.e. head sparing growth retardation) and the placenta is large and cystic with molar changes. If the extra set is maternal in origin (digyny) the fetus is severely growth retarded and the placenta is small. Syndactyly is frequently present between the third & fourth fingers.

The other major problem with pregnancies affected by triploidy is hydatidiform molar changes in placental tissue. A hydatidiform mole is a proliferation, or overgrowth of placental tissue, such that there is over production of the hormones of pregnancy and often vaginal bleeding early in pregnancy, present like a miscarriage. Molar changes in the placenta can co-exist with an on-going pregnancy, but more commonly there is no fetus in these pregnancies, and they are managed by evacuation of the uterus and followed up with hormone analysis to ensure they have not recurred.

Suspicions of a viable pregnancy affected by polyploidy are usually first raised by fetal growth failure, which happens early in pregnancy and is severe. Structural anomalies including cardiac malformations can occur, but many cases with have no obvious structural abnormality on ultrasound assessment. If caesarean section delivery is being contemplated for severe growth restriction it is wise to consider chromosome analysis, if circumstances permit. If triploidy, or another lethal diagnosis is made it is logical to avoid caesarean section delivery if possible, accepting the inevitability of the death of the baby.

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Most cases are lost spontaneously in the second or third trimester but some liveborn and die in the neonatal period. Liveborn infants are severely retarded and other associated anomalies include craniofacial abnormalities, brain anomalies, and eye defects. Affected males have genital anomalies including hypospadias and cryptorchidism.

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To be added

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© Perinatal Institute 2011