A study on 85 pregnancies with chromosome abnormality diagnosed by prenatal cytogenetic analysis

There is no doubt that, in the last decades,conventional cytogenetics has been a powerful tool for early prenatal diagnosis (PD). The present report describes chromosomal aberrations in 85 cases referred to our private laboratory for PD in a period between 1999-2002.
Amniocentesis (AC) and chorionic villus sampling (CVS) were two methods employed to obtain samples for cytogenetic analysis. Of 85 samples with abnormal karyotypes, 84 came from AC, while only 1 was from CVS. Of those, 41 were numerical (35 trisomies, 3 sex chromosome aberrations and 3 triploidy) and 44 were structural aberrations. The distribution of the results is given: Down syndrome (DS) (total= 33, trisomy 21,n=30, mosaic n=l, t(l4;21) type n=l, t(21;21) type n=l), trisomy 18 (n=3), mosaic trisomy 20 (n=l), 69,XXX (n=3), Turner syndrome (n=2), 47,XXY (n=l), +mar (n=2), balanced reciprocal translocation (n= 13), pericentric and paracentric inversions (n=6), and pericentric inversion 9 (n=18). The major indications were advanced maternal age (42.5 %), positive triple test (TT) (37.0%), ultrasound abnormalities (11.1%), recurrent miscarriages (5.5 %), parental structural rearrangement(1.8%), and previous chromosomal abnormality (1.8%). Maternal age ranged between 18-47 (mean=34). Of those who had fetus with Down syndrome, 12 were below 35 year of age, and 14 were above 35. indications for the diagnosis of DS were advanced maternal age (48.3%), positive triple test (TT) (34.5%), ultrasound abnormalities (10.3%), and recurrent miscarriages (6.9%). Of those with ultrasound abnormalities, nuchal thickness was the major finding indicating DS (66%). Pregnancies with abnormal karyotypes (n=4l) were terminated following a written consent of the families. On the other hand, those with balanced chromosome changes were not terminated.
The study cleaıiy demonstrates that cylogenetic analysis should be indicated in a situation that there is even little suspicion for high risk pregnancy. We can conclude that:
1. Average maternal age for DS child is 34.
2. Advanced maternal age was the most frequent indication for PD (42.5%).
3. Maternal age and İT still remain as significant indicators for chromosome analysis.
4. Approximately 50% of the chromosome abnormalities are structural abnormalities. This means that DS itself is not a single indication for prenatal cytogenetic analysis.
5. Prenatal ultrasound is not a method of first choice for the diagnosis of DS. Because majority of DS cases revealed by cytogenetic analysis were normal at ultrasound controls.
6. Nuchal thicness is an important finding indicating prenatal cytogenetic diagnosis

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