What is a all chromosome test?
While early NIPT mainly tests for chromosome 21, 18 and 13 trisomies, Hiro Clinic’s all-chromosome aneuploidy test is an advanced diagnostic method compared to early NIPT.
Our next-generation method comprehensively tests for abnormalities (aneuploidy) in chromosomes 1-22 and the entire sex chromosome, and reports on the chromosomes with abnormalities. This method has attracted increasing attention in recent years and provides more comprehensive genetic information.
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If an abnormality is found in a chromosome other than chromosomes 21, 18 or 13 trisomy, the chances of survival may be reduced.
In particular, abnormalities in chromosomes other than chromosomes 13, 18 and 21 autosomes can seriously affect the maintenance of life. Comprehensive testing for these chromosomes is therefore important.
Global prenatal testing guidelines recommend a more extensive and comprehensive screening for chromosome abnormalities, including information on sex chromosomes, which is not available using traditional diagnostic methods. Conventional prenatal diagnosis focuses mainly on the three autosomes, but it has been reported that problems with the sex chromosomes can occur even in the absence of abnormalities in these chromosomes.
It is estimated that approximately 0.56% (approximately 1 in 200) of chorionic villus biopsies and 0.05% (approximately 1 in 2000) of amniotic fluid tests are positive. This could have been missed by conventional methods, and total chromosome aneuploidy testing is an important means of reducing this uncertainty.
Why pregnant women over 35 years of age are the standard
Early NIPT was previously only available for pregnant women over 35 years of age to undergo NIPT.
The reason for this is that the incidence of sex chromosome abnormalities changes after the age of 35.
At Hiro Clinic, test results are tabulated for women aged 19-51 who have undergone NIPT testing. The target age for older births is defined as 35 years and over.
Of the 809 examinees with a positive result for 21 trisomy (Down syndrome), 613 are aged 35 years or older.
The image below shows that the number increases with age.
Positivity rates for total chromosome aneuploidy in chorionic biopsy and amniotic fluid testing
| 21, 18 and 13 trisomy | Other trisomy | |
|---|---|---|
| Number of samples in chorionic biopsy |
5.06% (532 out of 10,511) |
0.56% (59 out of 10,511) |
| Number of samples in amniotic fluid testing |
1.02% (748 out of 73,268) |
0.05% (30 out of 73,268) |
| Number of samples from both chorionic biopsy and amniocentesis tests |
2.1% (235 out of 11,066) |
0.12% (13 out of 11,066) |
1. Konialis C, Pangalos C. Dilemmas in prenatal chromosomal diagnosis revealed through a single center’s 30 years’ experience and 90,000 cases. Fetal Diagn Ther 2015; 38(3):218-232.
2. Comas C, Echevarria M, Rodríguez I, Serra B, Cirigliano V. Prenatal invasive testing: a 13-year single institution experience. J Matern Fetal Neonatal Med 2014 Aug;27(12):1209-12.
Reported positive by trisomy type for all chromosome aneuploidy test
（excluding mosaicism）
| Trisomy １ | Exhausted egg |
|---|---|
| Trisomy ２ | Incapable of survival |
| Trisomy ３ | No positive reports |
| Trisomy ４ | Rarely：Incapable of survival |
| Trisomy ５ | Incapable of survival |
| Trisomy ６ | Incapable of survival |
| Trisomy ７ | Incapable of survival |
| Trisomy ８ | Incapable of survival |
| Trisomy ９ | There are surviving cases |
| Trisomy 10 | Incapable of survival |
| Trisomy 11 | Incapable of survival |
| Trisomy 12 | Incapable of survival |
|---|---|
| Trisomy 13 | There are surviving cases |
| Trisomy 14 | Incapable of survival |
| Trisomy 15 | There are surviving cases |
| Trisomy 16 | Incapable of survival |
| Trisomy 17 | Incapable of survival |
| Trisomy 18 | Incapable of survival |
| Trisomy 19 | Extremely rare：Incapable of survival |
| Trisomy 20 | There are surviving cases |
| Trisomy 21 | There are surviving cases |
| Trisomy 22 | There are surviving cases |
FAQs about all chromosome testing
Q: Does an all chromosome test reveal all chromosomal abnormalities in the foetus?
To test for structural abnormalities such as chromosome deletions and duplications as well as abnormal numbers of chromosomes, an all-autosomal whole-region partial deletion/duplication disease test※ is required.
For more information on total autosomal partial deletion/duplication diseases, see ‘What is total autosomal partial deletion/duplication disease’.
※Limited, however, to anomalies of 7 million bases or more
