Increased nuchal translucency, hydrops fetalis or hygroma colli. A new test strategy for early fetal aneuploidy detection.
OBJECTIVE
Nuchal translucency measurement of 3 mm or more (> or = 95th centile for gestation age), hydrops fetalis or hygroma colli between the 11th and 14th weeks of gestation is associated with a higher risk of fetal Down syndrome and other aneuploidies. So far, chromosome preparation of chorionic villi samplings (CVS) after short-term (or direct) culture is the only valid, reliable and rapid method of choice for the early detection of chromosomal aberrations. However, because of the placental mosaicisms detected after short-term culture, CVS has to be confirmed by a second method. Moreover, short-term villi preparation does not always provide a sufficient quantity and quality of metaphases to enable cytogenetic analysis. Unfortunately, a predicative cytogenetic result will be available only after long-term cultivation (usually after 1-2 weeks). An alternative rapid method, inexpensive and suitable for diagnosing autosomal trisomies, is the quantitative fluorescence polymerase reaction (QF-PCR) using different polymorphic small tandem repeats (STRs) on CVS-DNA. Therefore, it was the aim of the study to evaluate whether a new CVS test strategy could be employed in early pregnancies at high risk after the rapid detection of fetal chromosomal abnormalities by QF-PCR for chromosomes 13, 18 or 21 and sexing in conjunction with short-term chromosome analysis.


METHODS
Nineteen CVS were chosen for QF-PCR detection of trisomy 21, 18 or 13 after an increased nuchal translucency measurement (> or = 95th centile for gestation age), a hydrops fetalis or a hygroma colli. The amelogenin locus of chromosomes X and Y (AMXY) were used for sexing. The QF-PCR results were compared with routine karyotyping after short- and/or long-term cultivation of CVS cells.


RESULTS
An informative result was demonstrated in all analysed specimens. Nine CVS were diagnosed as a QF-PCR trisomy either for chromosome 21, 18 and 13. The pathological samples also included 4 cases of mosaicism where the normal cell line was not identified by QF-PCR. In 1 additional case with a normal QF-PCR result, short-term CVS chromosome analysis showed a mosaic trisomy 13, whereas longterm CVS culture revealed a normal karyotype. The malformed aborted fetus showed no clinical signs of trisomy 13, confirming the normal results obtained by QF-PCR and long-term CVS chromosome analysis. One pregnancy with a Turner syndrome was not identified by molecular analysis.


CONCLUSIONS
This study showed that all early pregnancies with a clinically relevant autosomal trisomy could be detected prenatally in routine practice by QF-PCR. The combined use of both rapid methods - QF-PCR and short-term chromosome analysis - optimise the results by minimising the possibility of false-positive or false-negative findings. We believe that after verification of a pathological result obtained by two independent methods (QF-PCR and short-term CVS chromosome analysis), long-term villi cultivation is no longer necessary. However, in all cases with discrepancies, especially in samples with mosaic findings at short-term CVS cultivation, further studies are still necessary.
Jenderny
J
J
Institute of Immunology, Pathology, Molecular Biology and Human Genetics, Department of Prenatal Diagnostic and Therapy, Hamburg, Germany. jenderny@labor-keeser-arndt.de
Schmidt
W
W
Hecher
K
K
Hackelöer
B J
BJ
Kerber
S
S
Kochhan
L
L
Held
K R
KR
D015193:Chorionic Villi Sampling; D004314:Down Syndrome / Q000150:complications / Q000175:diagnosis*; D005260:Female; D006801:Humans; D015160:Hydrops Fetalis / Q000150:complications / Q000000981:diagnostic imaging*; D018191:Lymphangioma, Cystic / Q000150:complications / Q000151:congenital* / Q000000981:diagnostic imaging*; D009030:Mosaicism; D016133:Polymerase Chain Reaction; D011247:Pregnancy; D016216:Ultrasonography, Prenatal