Abnormal results in prenatal tests could mean problems with mom
For pregnant women, abnormal results from certain prenatal tests may signal that something is wrong – with the moms-to-be, not the foetus, a preliminary study suggests.
Very rarely, these results may indicate cancer in the women when follow-up testing shows the foetus is healthy.
The non-invasive tests are increasingly being used to detect foetal chromosome abnormalities, including Down syndrome. They test pregnant women’s blood, which contain small amounts of foetal DNA. But cancer is among conditions that can cause results that mistakenly indicate an abnormality in the foetus, the researchers say. The results are not definitive, although smaller studies have had similar findings.
The research was published online Monday in the Journal of the American Medical Association:
The study involved blood tests from more than 100,000 women, processed over nearly three years by a Redwood City, California laboratory. Nearly 4,000 women, or about three per cent, had results suggesting foetal chromosome abnormalities. In 10 cases, the babies turned out to be healthy but the women were later diagnosed with cancer, including lymphoma, leukaemia and colon cancer.
The study focused on eight of these women, who were diagnosed within weeks to several months of the test.
Most had prenatal tests suggesting more than one chromosome abnormality in the baby. In three women, cancer was diagnosed during a medical work-up prompted by the prenatal test results. Other cancers were discovered after women developed symptoms. Two women had advanced cases.
Non-invasive prenatal tests for foetal chromosome abnormalities are increasingly being recommended for women at high risk of having a child with Down syndrome; about two million tests have been performed worldwide, lead author Dr Diana Bianchi said. False-positive results are rare; they occur in just 0.2 per cent of tests at the lab involved in the study, said Bianchi, executive director of Tufts Medical Centre’s Mother Infant Research Institute.
False-positives can occur for several reasons, including a twin pregnancy when one twin dies, and when the mother has a transplanted organ from a male donor. Cancer cells shed DNA that the tests can detect. It’s a rare cause of false-positives but Bianchi said more definitive data are needed to determine the incidence.
“We don’t know how many people are walking around with silent cancers this test is accidentally uncovering,” Bianchi said. Women should be aware of the possibility when they seek the prenatal tests, and when results suggest a foetal problem, follow-up testing including amniocentesis is recommended.
But Bianchi said it would be premature to recommend cancer testing for all women whose tests have false-positive results.
A JAMA editorial says more rigorous research is needed to help doctors determine how to counsel these women.
