By Clare Wilson

Many pregnant women are eager to know exactly when they will give birth, and one day a blood test might be able to tell them.

At the moment, women are given a due date that is 40 weeks from the first day of their last period, but some give birth weeks before that, while others go beyond that date and may need to have labour induced.

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Ina Stelzer at Stanford University, California, and her colleagues are investigating a new approach that involves tracking how the body responds to signals from the fetus and prepares for labour. “The blood shows that birth is approaching,” she says.

Stelzer’s team took blood samples from 53 pregnant women and tested them in multiple ways between one and three times over their expected last 100 days of pregnancy. The researchers looked at nearly 5000 biochemicals and carried out more than 2000 tests on immune cells in their blood.

Two to four weeks before the birth, the team found that there was a change in the women’s hormone patterns and a fall in inflammatory immune cell activity, reflected by changes in the blood biomarkers.

The researchers built a prediction model using 45 of the biomarkers and tested this on a further 10 women. It predicted a probable delivery date that for each of them was within 17 days of their actual date, either before or after. Stelzer believes that as results from more women are added to the model it will become more accurate. The researchers haven’t yet tested if the model would work for multiple pregnancies or pregnant trans men.

If turned into a commercial test, it could be useful for knowing if pregnant women are likely to give birth prematurely, says Rachel Tribe at King’s College London (KCL). At the moment this requires taking a swab of their vaginal fluid and doing a scan to measure the position of their cervix.

Such a test could also help if doctors are worried about a fetus’s condition and want to know if birth is imminent or if they need to induce labour, says Andrew Shennan, also at KCL.

Journal reference: Science Translational Medicine, DOI: 10.1126/scitranslmed.abd9898

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