Prenatal testing can give expectant parents insight into the health of their unborn child, but the tests are not foolproof. A new wider use of gene testing in early pregnancy that involves scanning the genes of a fetus can give more accurate results about potential health risks than current prenatal testing.
A study published this week in the New England Journal of Medicine compared current prenatal testing to gene scanning and found that a surprisingly high number – 6 percent – of fetuses that were found to be normal by conventional testing were found through gene scans to have genetic abnormalities. These abnormalities ranged from minor defects such as club foot, to more serious defects like mental retardation, heart defects, and fatal diseases.
Conventional prenatal tests involve an untrasound exam or a blood test that can show some common abnormalities that could signal conditions such as Down syndrome. However, these tests are not conclusive.
The next step involves diagnostic testing on cells obtained from an amniocentesis, or fetal tissue from chorionic villus sampling. These samples are examined through microscopes for any breaks or extra chromosomes, which can signal a dozen or so more abnormalities. The new method involves scanning genes with a chip that can identify hundreds of abnormalities and smaller defects than what can be seen through a microscope.
The study comparing the new scanning with convention testing involved fetal samples from 4,400 women. Half of the mothers were considered higher risk because they were older than age 35. One-fifth of the mothers had screening tests that suggested Down syndrome. A quarter of the women had ultrasounds suggesting structural abnormalities.
Some women chose to undergo testing to settle anxieties. Gene scans showed abnormalities in 1 in 17 of the women whose ultrasounds showed a possible structural defect but whose fetuses were deemed “normal” through the visual chromosome exam.
“That’s a lot. That’s huge,” said Dr. Susan Klugman with New York’s Montefiore Medical Center.
In a separate study published in the New England Journal of Medicine, gene scanning of fetuses could also give insight into why stillbirths occur. That study involved 532 stillbirths, or deaths of a fetus in the womb before delivery. Gene testing found the cause of death in 87 percent of the cases compared to 70 percent of the cases analyzed by the visual chromosome method. Gene scanning also gave more details on specific gene abnormalities that parents could use to estimate the odds of risks with future pregnancies.