Unexpected Prenatal Cytogenetic Results in Positive Maternal Serum Screening Cases

摘要

Maternal Serum Screening (MSS) in 1st and 2nd trimester of pregnancy is a known and voluntary accepted screening method for chromosome 18, 21 and Neural Tube Defect (NTD) in the general population. Every screening method is supported by a diagnostic test and hence, in screen positive (high risk) cases, confirmation of the chromosomal anomaly requires invasive procedures like Chorionic Villus Sampling (CVS), Amniocentesis or Cord Blood Sampling. Genetic Counseling before the sample collection plays an important role for the couple to make an informed choice for which the consent is obtained. Trisomy of Chromosome 13, 18, 21 are the common findings in high risk cases with positive MSS. Unusual chromosome anomalies also come as a surprise. The present study is of 1329 high risk maternal serum screen positive cases with average gestational age of 17-18 wks for whom Amniocentesis was done to rule out chromosomal aneuploidies only. Of the total 1392 cases, 82 abnormalities were observed. In 47 (57.32%) cases, expected chromosomal aneuploidy (Trisomy of chromosome 13, 18 and 21) were seen. Unexpected results were observed in 35 (42.68%) cases. The unexpected results included Monosomy, Trisomy of sex chromosomes, Translocation, Inversion of autosomal and sex chromosome, Deletion, Duplication, Isocentric, Marker chromosomes and derivatives. The high number of unexpected finding is sufficient enough to conclude the importance of Genetic Counseling and fetal Karyotyping in prenatal diagnosis.