Tissue-specific mosaicism among fetuses with prenatally diagnosed diaphragmatic hernia.

Objective: Our purpose was to determine if cytogenetic discrepancies between fetal blood and amniotic fluid are present in fetuses with prenatally diagnosed diaphragmatic hernia.

Study Design: Chromosome analysis was performed on 15 fetuses with prenatally diagnosed diaphragmatic hernia. Fourteen had both amniotic fluid and fetal blood studies. One fetus had an amniocentesis followed by postnatal skin and peripheral lymphocyte chromosome analysis.

Results: In one fetus with a normal karyotype on fetal blood, amniotic fluid mosaicism for a supernumerary isochromosome 12p was identified. Another fetus had normal amniotic fluid chromosome analysis but was diagnosed with mosaic isochromosome 12p on skin biopsy after birth. Concordant aneuploidy in both fetal blood and amniocytes was found in five pregnancies (three with trisomy 18, one with an unbalanced translocation, and one with mosaic supernumerary isochromosome 12p). Eight fetuses had normal karyotypes.

Conclusion: Because diaphragmatic hernia is a common component of mosaic isochromosome 12p syndrome and this chromosome abnormality is predominantly found in fibroblasts but not lymphocytes, an amniocentesis may be more accurate than fetal blood sampling in defining the true fetal chromosome status when diaphragmatic hernia is detected prenatally.