In Rehri Goth, a fishing settlement on the outskirts of Karachi, Pakistan, roughly one in four babies is born prematurely, nearly double the country's national average and among the highest rates recorded anywhere in the world. Researchers say the crisis matters because premature birth is a leading driver of infant mortality in low-income settings, with around half of babies born at 32 weeks in such communities failing to survive, and the scale of the problem in this one community has drawn scientists seeking to understand why it is so much worse than in comparably poor areas elsewhere.

Investigators from Agha Khan University point to a mix of environmental and biological factors: maternal malnutrition, extreme heat above 113°F, and sewage-contaminated water in a settlement with poor sanitation. Crucially, they also found that mothers who delivered prematurely had markedly lower levels of a gut bacterium called Prevotella copri than those who carried to term, a discovery researchers hope could lead to a probiotic-style intervention for at-risk pregnant women. Dr Fyezah Jehan, involved in the research, noted that other countries share similar conditions without such high prematurity rates, and argued that improving education, water and sanitation "would make half the problems just disappear."