Indigenous Infant Mortality by Age and Season of Birth, 1800–1899: Did Season of Birth Affect Children’s Chances for Survival?

Abstract

This paper focuses on the influence of season of birth on infant mortality among the Sami and non-Sami populations in northern Sweden during the nineteenth century. The source material is a set of data files from the Demographic Data Base at Umeå University, making it possible to combine age at death (in days), month of death, and month of birth over the course of the entire century. Cox regression models reveal that for the first week of life, season of birth had no influence on the risk of mortality. For the Sami, the results showed that being born during winter was related to a higher risk of neonatal mortality, and being born during summer was related to a higher risk of mortality after six months of age. Furthermore, for the Sami, the neonatal mortality showed a U-shaped pattern with a minimum in June–August, whereas the corresponding pattern among the non-Sami was flatter. The findings shed light on vulnerability in two populations sharing the same environment, but diverging in terms of social, economic, and cultural factors.

Season of birth, stillbirths, and neonatal mortality in Sweden: the Sami and non-Sami population, 1800–1899

“…We previously showed that the season of birth indicated differential effects depending on age at death among Sami populations in the parishes of Jokkmokk and Jukkasjärvi in Swedish Sápmi [25]. Being born during winter was related to a higher risk of neonatal mortality, while being born during summer was related to a higher risk of mortality after 6 months of age [25]. These results implied that infant mortality risks are generally higher during winter and are also related to sensitive stages during the first year of life, both as new-borns during the neonatal period and around the age of six months when food was introduced in combination with the waning effect of maternal antibodies.…”

“…Seasonality, neonatal mortality, and stillbirths Previous research of neonatal mortality in Swedish Sápmi has revealed that Sami infants born during the summer months (July and August) had the highest neonatal mortality risk, whereas the non-Sami infants showed no seasonal differences [7]. We previously showed that the season of birth indicated differential effects depending on age at death among Sami populations in the parishes of Jokkmokk and Jukkasjärvi in Swedish Sápmi [25]. Being born during winter was related to a higher risk of neonatal mortality, while being born during summer was related to a higher risk of mortality after 6 months of age [25].…”

“…A model of seasonality, stillbirths, and neonatal mortality We expected that the Sami had a higher neonatal mortality than the non-Sami, but that neonatal mortality rates within each population varied by season, based on the mother's seasonal workload. Following previous research on seasonality and infant mortality in Sápmi [25], we hypothesised that winter-born Sami infants had the greatest risk of neonatal mortality, whereas infants born in summer experienced the lowest levels.…”

The association between cold extremes and neonatal mortality in Swedish Sápmi from 1800 to 1895

“…From previous research on infant mortality in historical populations, we know that the season of birth affects the risk of infant mortality and season of birth is, therefore, a good proxy for living conditions in utero and during early infancy [8,12]. Neonatal mortality also appears to be associated with the seasonality of infectious diseases and extreme temperatures, e.g.…”

“…Generally, the infant mortality rate was higher among the Sami population compared to the non-Sami population until 1860, after which the differences decreased over time [5]. Comparing seasonal patterns of neonatal mortality during the nineteenth century, the mortality rate was higher during the winter for Sami and non-Sami populations [8]. How these seasonal patterns changed over time and in relation to temperature differences during the winter is still unknown.…”