Screen all chromosomes in prenatal embryo testing, says study

Current prenatal chromosome screening tests could miss rare chromosomal abnormalities and lead to inaccurate results.

Non-invasive prenatal testing (NIPT) analyses fetal DNA in the mother's blood, and is increasingly used to screen embryos for trisomies, which can cause pregnancy complications or serious health conditions. Yet currently, NIPT considers only the chromosome pairs which most commonly have trisomies - 13, 18, 21 and the sex chromosomes - and researchers say this may miss valuable information.

'Extending our analysis to all chromosomes allowed us to identify risk for serious complications and potentially reduce false-positive results for Down syndrome and other genetic conditions,' said senior author Dr Diana Bianchi, director of the National Institute of Child Health and Human Development, USA.

Researchers in the US and Australia set out to investigate how chromosomal abnormalities are being picked up by standard NIPT analyses. NIPT works by comparing counts of chromosomes from fetal DNA with a set of 'reference' chromosomes in the same sample. However, if there is an abnormality in the reference chromosomes, the test may fail or return abnormal results.

The team looked at data from nearly 90,000 pregnancies, of which 627 cases were flagged up as abnormal or borderline by standard NIPT. They found rare trisomies were only detected if all genome data obtained by a NIPT test was analysed.

Out of the 627 cases, they found 399 carried rare trisomies most commonly found in chromosomes 7, 15, 16 and 22, and a considerable proportion of rare trisomies affected reference chromosomes.

'Although these trisomies are relatively rare they can be associated with serious pregnancy health problems,' lead author Dr Mark Pertile at the Murdoch Children’s Research Institute in Melbourne, Australia told the Herald Sun. 'We found that sometimes these chromosomes conditions were affecting only the placenta not the baby and that could impact the normal growth of the pregnancy.'

The researchers were able to combine some of this genetic information with clinical data about pregnancy outcomes. Of 52 cases with rare autosomal trisomies, 22 were linked to early miscarriage.

'Our results suggest that patients be given the option of receiving test results from all 24 chromosomes,' said Dr Pertile.

The study, published in Science Translational Medicine, is the largest of its kind and involved both academic researchers and biotech companies Illumina and GRAIL in Redwood City and Menlo Park, California.

The results of the study have already been translated into clinical practice, with Illumina’s Verfi Plus test and the Victorian Clinical Genetics Service’s Percept test both offering screening of all chromosomes. This should help medical professionals better identify which pregnancies should be closely monitoring and when to offer genetic counselling.