Jun 11th 2025
WHEN NON-INVASIVE prenatal testing (NIPT) arrived in 2011, it transformed pregnancy. With a simple blood test, scientists could now sweep a mother’s bloodstream for scraps of placental DNA, uncovering fetal genetic defects and shedding light on the health of the unborn baby. But the potential to monitor the mother’s health went largely unappreciated.
A decade of advances in genetic sequencing and machine learning is now unlocking that potential, says Gavin Ha, a computational biologist at Fred Hutchinson Cancer Centre in Seattle. Scientists are now using prenatal tests to look for hidden cancers and predict dangerous complications of pregnancy such as pre-eclampsia and preterm births.
NIPT tests work by scouring the mother’s blood for DNA fragments and mapping them to their chromosome of origin. Around 10% of these fragments come from the placenta, which usually has identical DNA to the developing fetus. If the percentage of DNA linked to a particular chromosome is unusually high or low, and doctors know the pregnant woman does not have the associated genetic condition, it may point to a fetal abnormality. Though such tests are routinely offered in rich countries from the tenth week of pregnancy onwards, approximately three in 1,000 results come back as inconclusive.
In a study published in December in the New England Journal of Medicine, a team of American researchers gave full-body MRI scans to about 100 women with such inconclusive findings. In half of these cases, the results were linked to false positives, maternal conditions such as fibroids, fetal and placental abnormalities or some unknown cause. In the other half, the scans revealed the mothers had cancer. The prenatal-test results had been scrambled by tumour DNA shed into their bloodstream.
The results are of interest because, at present, spotting cancer in pregnant women is extremely difficult. They are not seen as an at-risk group, and their symptoms are typically chalked up to the normal difficulties of pregnancy, says Catharina Heesterbeek, an oncologist at Maastricht University Medical Centre who led a similar study in 2022. A standard prenatal test could thus find cancers that would never otherwise have been discovered.
Dangerously high blood pressure during pregnancy, otherwise known as pre-eclampsia, is an even greater threat. As its onset is hard to predict, women often have to wait until the second or third trimester to see if they have it. Prenatal tests might be able to help improve matters.
In a paper published in Nature Medicine in February, Dr Ha and his colleague Raj Shree, a doctor at the University of Washington, used a machine-learning algorithm to categorise DNA from standard prenatal tests of almost a thousand women. Their findings showed that, compared with healthy mothers, pregnant women who go on to develop pre-eclampsia have slightly less placental DNA in their blood, and slightly more DNA from the lining of their blood vessels. Their model could predict pre-eclampsia with 80% accuracy by the 16th week of pregnancy, well before clinical signs appeared.
Prenatal tests could even predict a woman’s chances of giving birth prematurely. Most such births happen spontaneously, due to inflammation, abnormal placental development and other stressors, but the presence of certain proteins in the bloodstream can serve as early-warning signals. Recent studies show that testing pregnant women’s blood for these proteins, or the molecules regulating their production, can lead to almost 90% of preterm births being predicted between weeks six and 20 of pregnancy.
The clinical landscape is beginning to adapt. The Netherlands and Belgium now offer genetic counselling and whole-body MRIs to anyone with inconclusive prenatal-test results, says Merryn Macville, a clinical-laboratory geneticist at Maastricht University Medical Centre. American biotech companies including Mirvie and Sera Prognostics are selling pre-eclampsia and preterm-birth tests directly to consumers, at costs ranging from $750 to $1,850.
Early detection does not always translate into prompt treatment. Many common cancer therapies, including chemotherapy and surgery, can be extremely risky during pregnancy. Similarly, the only proven method to reduce the risk of pre-eclampsia and preterm births is a course of aspirin, which is already widely recommended for pregnant women, says Baha Sibai, a maternal-fetal medicine specialist at the University of Texas Health Sciences Centre.
Additional screening also comes with risks. The more tests a patient undergoes, the greater the chances of a stress-inducing false positive and unnecessary follow-up tests. That means the real benefits for maternal health might be indirect. Identifying mothers most at risk of pre-eclampsia and other dangerous conditions could help doctors design more targeted clinical trials and, ultimately, develop better treatments and prevention strategies. In the long run, that could allow prenatal testing to live up to its life-saving potential. ■
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