The weeks before a baby's due date can feel like the longest stretch of a pregnancy. Most parents picture the birth landing at a familiar point on the calendar. For about one in ten families in the United States, the baby decides otherwise.
Researchers at UC San Francisco have found immune-system antibodies that appear earlier and at higher levels in women who later give birth before 37 weeks.
The finding, published in October 2026 in Nature Immunology, points to an autoimmune pathway as a possible trigger for some early deliveries.
Preterm birth is one of the leading causes of newborn death and long-term disability. According to the CDC, 10.41 percent of US babies were born before 37 weeks in 2024, unchanged from the year before.
Also read: 7 everyday habits that may quietly be raising your risk of liver damage
What the antibody signal looked like
The team analyzed blood samples from more than 2,000 pregnant women across eight separate groups. One set of samples was drawn at 15 weeks of pregnancy through California's statewide prenatal screening program.
Women who later delivered preterm showed broader antibody changes earlier in pregnancy than women who delivered at term. Among those antibodies, one stood out.
It targeted a protein called IL-1RA, short for interleukin-1 receptor antagonist. IL-1RA's normal job in the body is to keep inflammation in check.
Why IL-1RA matters for pregnancy
IL-1RA works as a brake on another protein, IL-1 beta, which drives inflammation and is known to trigger uterine contractions. The pregnancy relies on that brake to stay stable.
Also read: Brain bleed history no longer means ruling out blood thinners for AFib, new data suggests
"The placenta is basically stocking up on this inhibitor to protect the pregnancy," said Elze Rackaityte, who led the work and is now an assistant professor at UCSF, according to GEN.
An antibody that neutralizes IL-1RA removes that brake. Inflammation can then build up unchecked, and so can the signals that start labor.
To test the idea, the team injected the IL-1RA antibodies into pregnant mice. IL-1 beta levels rose in the mothers' blood, and the placentas showed damage patterns similar to those seen in human preterm deliveries.
What this could mean for future treatments
This is early-stage mechanistic research, not a diagnostic test. The anti-IL-1RA antibodies showed up in only a fraction of preterm cases, so other causes are likely at work in most early deliveries.
Also read: Air pollution may be quietly raising your blood sugar even if you don't have diabetes
But a synthetic form of IL-1RA already exists as an approved medicine. Anakinra, used for rheumatoid arthritis, has nearly two decades of safety data behind it.
That makes it a logical candidate to investigate as a possible preventive treatment in pregnancies flagged as high risk.
A diagnostic test or a clinical trial of anakinra in high-risk pregnancies would need years of further research before any such treatment reached patients.
Also read: Two drugs you may have in your medicine cabinet just entered an Alzheimer's trial
Also read: 7 warning signs your vitamin D may be dropping as the days get shorter
This article is made and published by Aksel Kryhlmand, who may have used AI in the preparation.