In Italy, hot days were linked to lower fertility nine months later

The association was strongest in provinces with higher incomes and fewer healthcare workers.

Editorial illustration — not from the study.

Researchers matched monthly birth registration data from 107 Italian provinces with temperature and other weather records covering 2003–2022. They examined whether exposure to hot days—defined as days with a mean temperature above 25 °C—was related to total fertility rates nine months later.

The analysis found that hot-day exposure was associated with a relatively immediate reduction in the probability of conception, reflected in lower fertility rates nine months afterward. The largest effects appeared in provinces with above-average GDP and in those with lower-than-average healthcare workforce availability.

What the heat was linked to

Exposure to hot days, defined as days with a mean temperature above 25 °C, was associated with lower total fertility rates nine months later across Italy’s 107 provinces. The study describes the effect as relatively immediate in terms of conception probabilities. The association was largest in provinces with above-average GDP and in provinces with lower-than-average healthcare workforce availability.

Why the finding matters

Italy already has low fertility, and the country has also experienced climate change alongside sharp regional differences in climate and economic conditions. The findings suggest that periods of high temperatures may be linked to fertility changes, with the strongest associations appearing in areas where healthcare workforce availability was lower. This makes local differences in heat exposure and healthcare resources relevant when considering climate-related pressures on reproductive health.

Evidence and caveats

This was a province-level analysis that matched monthly birth registration data with meteorological records from 2003 to 2022. It identifies relationships between heat exposure and later fertility rates, but the abstract does not establish the individual mechanisms involved or show that heat directly caused the changes. Because the analysis focused on Italian provinces, its findings may not apply in the same way to other countries or settings.

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