Background: Climate vulnerability of the unborn can contribute to adverse birth outcomes, in particular, but it is still not well under-stood. We investigated the association between ambient temperature and stillbirth risk among a historical population in northern Sweden (1880–1950).
Methods: We used digitized parish records and daily temperature data from the study region covering coastal and inland communi-ties some 600 km north of Stockholm, Sweden. The data included 141,880 births, and 3,217 stillbirths, corresponding to a stillbirth rate of 22.7 (1880–1950). The association between lagged temperature (0–7 days before birth) and stillbirths was estimated using a time-stratified case-crossover design. Incidence risk ratios (IRR) with 95% confidence intervals were computed, and stratified by season and sex.
Results: We observed that the stillbirth risk increased both at low and high temperatures during the extended summer season (April to September), at −10°C, and the IRR was 2.3 (CI 1.28, 4.00) compared to the minimum mortality temperature of +15°C. No clear effect of temperature during the extended winter season (October to March) was found. Climate vulnerability was greater among the male fetus compared to the female counterparts.
Conclusion: In this subarctic setting before and during industrialization, both heat and cold during the warmer season increased the stillbirth risk. Urbanization and socio-economic development might have contributed to an uneven decline in climate vulnerability of the unborn.