Weather extremes and perinatal mortality – Seasonal and ethnic differences in northern Sweden, 1800-1895

Abstract

BackgroundMany studies have shown the impact of heat and cold on total and age-specific mortality, but knowledge gaps remain regarding weather vulnerability of very young infants. This study assessed the association of temperature extremes with perinatal mortality (stillbirths and deaths in the first week of life), among two ethnic groups in pre-industrial northern Sweden.MethodsWe used population data of indigenous Sami and non-Sami in selected parishes of northern Sweden, 1800–1895, and monthly temperature data. Multiple logistic regression models were conducted to estimate the association of cold (<10th percentile of temperature) and warmth (>90th percentile) in the month of birth with perinatal mortality, adjusted for cold and warmth in the month prior birth and period, stratified by season and ethnicity.ResultsPerinatal mortality was slightly higher in Sami than in non-Sami (46 vs. 42 / 1000 live and stillbirths), but showed large variations across the region and over time. Both groups saw the highest perinatal mortality in autumn. For Sami, winter was a high-risk time as well, while for non-Sami, seasonality was less distinct. We found an association between exposure to cold and perinatal mortality among winter-born Sami [Odds ratio (OR) 1.91, 95% confidence interval (CI) 1.26–2.92, compared to moderate temperature], while there was little effect of cold or warmth during other seasons. Non-Sami, meanwhile, were affected in summer by warmth (OR 0.20, CI 0.05–0.81), and in autumn by cold (OR 0.39, CI 0.19–0.82).ConclusionsIn this pre-industrial, subarctic setting, the indigenous Sami’s perinatal mortality was influenced by extreme cold in winter, while non-Sami seemed to benefit from high temperature in summer and low temperature in autumn. Climate vulnerability of these two ethnic groups sharing the same environment was shaped by their specific lifestyles and living conditions.

Neonatal Mortality and Temperature in Two Northern Swedish Rural Parishes, 1860–1899—The Significance of Ethnicity and Gender

“…In this paper, we studied the association of daily temperature and seasonality with neonatal mortality, covering a sensitive period of an infant's life. Our previous studies, based on monthly mean temperatures, showed that Sami perinatal and neonatal mortality were influenced by extreme cold in the winter, whereas extreme cold winter temperature had no effect on the non-Sami population [6,8].…”

“…Based on information about family name, parish, occupation and family relations, an ethnical indicator that distinguished between the Sami population and the non-Sami population has been developed [39]. This ethnical indictor has been used in a variety of studies regarding marriage, fertility and mortality patterns in Swedish Sápmi [4,[6][7][8]13,23,39,40]. The available information about ethnicity does not allow a differentiation between nomadic and settled Sami.…”

“…Previous research of cold-related mortality has mainly used season of birth as a proxy for temperature or monthly mean temperatures from remote weather stations [6][7][8]. To our knowledge, this is the first study to examine the association between temperature and neonatal mortality in Sweden during the nineteenth century using local daily temperature data.…”

Socioeconomic disparities in climate vulnerability: neonatal mortality in northern Sweden, 1880–1950

“…According to previous findings regarding the effect of temperature on neonatal health in sub-Arctic areas (Karlsson et al, 2020;Schumann et al, 2019), we expected a strong impact of low temperatures, especially among more resource-poor groups (farmers and workers) that would diminish over time. A declining effect was not clearly discernible in any social group due to the low vulnerability observed in the first decades of the twentieth century.…”

Born in winter or spring more susceptible to all-cause and cardiovascular disease death in rural areas of China: results from a 11.9-year follow-up study

“…It was uncertain what explain the current results although there were several factors which might be important. Firstly, several researches reported that winter was a high-risk time, perinatal and neonatal mortality was influenced by extreme cold in winter [ 20 , 21 ], and January is the coldest month of winter in China. Secondly, many studies have demonstrated a link between early life nutrition and cardiovascular health and mortality in adulthood [ 22 , 23 ].…”