Introduction: The goal of cytogenetics is the detection of chromosomal abnormalities, achieved by the analysis of adequate numbers of metaphases at the appropriate bands per haploid set (BPHS).Clinical Picture: Two cases presented here include a foetal blood sample (FBS) of a 33-week-old referred with holoproscencephaly by ultrasonography, and an amniotic fluid (AF) specimen of a 14-week-old foetus with cystic hygroma, cardiac and renal defects.Outcome: The FBS had a deletion at 18p11.31. Another laboratory had earlier given a normal cytogenetic result on its AF sample. In the second case, an unbalanced 46,XY,der(5)ins(5;3) (q33.1;q26.2q27)mat karyotype was obtained with the AF sample. In both cases, the abnormalities were more obvious when band levels were ≥450 BPHS.Conclusion: This report underscores the importance of obtaining longer chromosome preparations above the current recommended 400 BPHS for prenatal specimens. This is particularly important in cases with abnormal ultrasound findings suggestive of an underlying chromosomal pathology.
Optimal chromosome preparation is a function of many factors. These include cell density culture initiation, optimal time for harvest, concentration and exposure duration to a mitotic arrestant, appropriate hypotonic treatment and adequate fixation with modified Carnoy’s fixative.
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