ABSTRACT
OBJECTIVE: Our purpose was to determine the distribution of karyotypic abnormalities detected at prenatal diagnosis, fetal anomalies, and ability for fluorescent in situ hybridization detection. STUDY DESIGN: Our cytogenetic database from January 1988 to April 1994 was categorized according to type and potential detection by current standard fluorescent in situ hybridization probes. Fetal anomalies and cytogenetic aberrations were compared. RESULTS: A total of 664 cases of abnormal fetal karyotypes were identified from 12,454 prenatal cytogenetic cases (7529 amniocenteses and 4925 chorionic villus sampling) and were classified as autosomal aneuploidy (331), sex aneuploidy (103), polyploidy (38), marker aneuploidy (19) and structural rearrangements (173). Standard fluorescent in situ hybridization probes would have missed 31% of the abnormal cases: 90 aneuploidy, 14 de novo marker aneuploidy, and 65 de novo structural aberrant cases. The 134 cases of structural chromosomal rearrangements with complete ultrasonographic records were further classified as polymorphism (42), familial (43), or de novo (49). Frequency of fetal anomaly detection by ultrasonography in de novo cases (22/49) was higher than other rearrangements (chi 2 7.4, p = 0.006). CONCLUSION: The contribution of unusual aneuploidies (16%) and structural chromosomal rearrangements (26%) in prenatal diagnostic practice is significant. Fetal anomalies were detected by ultrasonography in 45% of the de novo rearrangement cases. Fluorescent in situ hybridization would miss 31% of the abnormal cases.
