Every parent wants a healthy start for their baby. But for far too many families around the world, that beginning is marked by uncertainty. Each year, millions of babies are born too soon or too small—and for many, it’s a matter of life or death.
Globally, one in four newborns is either premature, has a low birth weight, or is small for their gestational age. These babies face a higher risk of complications and death during the first weeks of life. In fact, prematurity is now the leading cause of death in children under five.
What causes these poor outcomes? There are many factors, but one of the biggest culprits is often invisible: maternal infection and inflammation during pregnancy. This is particularly true for mothers living with HIV, whose babies are more likely to be born too early or too small.
A new study out of Zimbabwe suggests that one surprisingly simple intervention could help: a daily dose of a widely available antibiotic.
An international team of researchers led by Professor Andrew Prendergast from Queen Mary University of London and Bernard Chasekwa from the Zvitambo Institute in Zimbabwe wanted to know whether giving pregnant women a daily antibiotic called trimethoprim–sulfamethoxazole (TMP-SMX) could improve outcomes for their babies.
TMP-SMX is not new. It’s been used safely for decades to prevent infections, especially in people living with HIV. It’s inexpensive, easy to access, and has anti-inflammatory properties—which made it a strong candidate for reducing pregnancy complications linked to infection.
The trial, known as COMBI (Cotrimoxazole for Mothers to Improve Birthweight in Infants), included 993 pregnant women in rural Zimbabwe. Starting in their second trimester, the women were randomly assigned to receive either TMP-SMX or a placebo daily until delivery.
The researchers were primarily looking to see whether the antibiotic would increase birth weight. And on that front, the results were a bit disappointing. The babies in the TMP-SMX group weighed, on average, just 20 grams more than those in the placebo group—not a meaningful difference.
But when it came to preterm birth, the findings were far more compelling.
- Only 6.9% of women in the TMP-SMX group delivered prematurely (before 37 weeks).
- That’s compared to 11.5% in the placebo group.
- Not a single woman on TMP-SMX delivered before 28 weeks, whereas five in the placebo group did.
For a medication already in use and well understood, that’s a significant difference.
The impact was even more striking among the 131 women in the study who were living with HIV:
- Just 2% of HIV-positive women taking TMP-SMX delivered prematurely,
- Compared to 14% of those in the placebo group.
- Their babies were also, on average, 177 grams heavier.
While birth weight didn’t improve, the researchers believe this drop in preterm births deserves closer attention.
“Our trial, conducted within routine antenatal care and enrolling women predominantly from rural areas, showed that trimethoprim–sulfamethoxazole did not improve birthweight, which was our main outcome,” said first author Bernard Chasekwa. “However, there was an intriguing suggestion that it may have improved the length of pregnancy and reduced the proportion of preterm births.”
Professor Andrew Prendergast added:
“Our findings suggest that a low-cost, daily antibiotic, in a setting where infections like HIV are common, might reduce the risk of preterm births. We desperately need new strategies to prevent preterm births, which are the leading cause of under-5 child mortality.”
Sophie Hawkesworth from Wellcome, one of the study’s funders, emphasized the broader impact:
“If we are to reduce child mortality globally, it is critical to reduce the risk of preterm births, especially in areas with limited access to neonatal intensive care units. This is a promising study… the prospect that this treatment prevents preterm births warrants further study.”
In many parts of the world, early screening and treatment for infections during pregnancy is not always available. TMP-SMX could offer a simple, scalable solution—especially in regions where HIV is common and preterm birth rates are high.
What makes these findings so encouraging is that TMP-SMX is:
- Safe when used after the first trimester,
- Inexpensive (already widely distributed across sub-Saharan Africa),
- And easy to administer.
It’s not a new or experimental drug—it’s one that healthcare providers are already familiar with.
This study doesn’t offer a complete solution, but it opens a promising door. By focusing on length of pregnancy rather than just birth weight, it highlights a key point: a few extra weeks in the womb can be lifesaving.
While this was a well-designed randomized controlled trial, researchers note that further studies are needed:
- To confirm the link between TMP-SMX and reduced preterm birth,
- To test whether starting the medication earlier in pregnancy offers even more protection,
- And to assess outcomes in other countries and healthcare settings.
As Chasekwa put it, “We now need to repeat this trial in different settings around the world to see whether antibiotics during pregnancy can help reduce the risk of prematurity.”
This study didn’t deliver the result it originally set out to find—higher birth weights—but it may have uncovered something more important: a simple, affordable way to reduce the risk of premature birth.
In places where neonatal care is limited, preventing early delivery in the first place could make all the difference.
For now, the results are hopeful. If larger studies confirm these findings, TMP-SMX could become a valuable tool in reducing newborn deaths and helping babies around the world get a better start in life.
Sources:
- The New England Journal of Medicine, June 2025: A Trial of Trimethoprim–Sulfamethoxazole in Pregnancy
- Queen Mary University of London press release
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