Abstract for presentation at 11th International Congress of Human Genetics

Purpose: The possibility of a diagnostic, non-invasive, first trimester prenatal test may soon become reality. By testing at this early stage, common chromosome aneuploidies which often spontaneously abort prior to the second trimester will be encountered. In light of this, a 5-year review of products of conception samples was performed. This data will help formulate a strategy to maximise the detection of cytogenetic abnormalities seen during this period.
Methods: Data was gathered on 1556 samples over a 5-year period (2001-2005). This included reason for referral, maternal age, gestational age, and cytogenetic result. Standard culture methods were used.
Results: 1556 samples were submitted for analysis, with the majority submitted between 6-12 weeks gestation. 1375 (88%) samples were suitable for culture and results were obtained in 1250 cases (91% success). Male karyotypes of 46,XY were detected in 211 (16%) cases and 298 (24%) cases had a karyotype of 46,XX (including molar pregnancies). Abnormalities were detected in 741 (60%) cases. Autosomal Trisomy (64% of abnormalities) was seen for all chromosomes except 1 and 19. Trisomy 16 was the most common (16%), followed by trisomy 22 (9%) and trisomy 21 (8.5%). Other abnormalities included: triploidy/near triploidy (14%), monosomy X (10.9%), tetraploidy/near tetraploidy (3%), double autosomal trisomy (2.7%) and autosomal monosomy (0.4%). Structural chromosome abnormalities comprised 4% of abnormalities, with parental transmission seen in less than half of these cases (1.3%).
Conclusions: This data is generally consistent with previous literature. The majority of samples were received prior to the second trimester, when current prenatal diagnostic techniques are performed. A first trimester, non-invasive prenatal technique with the ability to detect changes in copy number for chromosomes 13, 16, 18, 21, 22, X and Y would detect approximately 75% of abnormalities found in this study.