Is increased size at birth associated with longevity on the population level? – A historical and comparative analysis of regions in Sweden

Increased population longevity could be influenced by early life factors. Some areas have long-lived populations, also in a historical perspective. We aimed to study these factors in Halland, an area with the highest life expectancy in Sweden. We collected archival data on gestational age and birth characteristics from 995 live singleton full-term births at the Halmstad Hospital, Halland, from the period 1936 to 1938 and compared these to 3364 births from three hospitals in nearby Scania for the period 1935–1945. In addition, data were obtained on maternal and offspring characteristics from the national Swedish Medical Birth Register during 1973–2013. The results show that when controlling for background maternal and offspring characteristics, mean birth weight (BW) and mean birth length were higher in Halland than in Scania, but the proportion of low birth weight (LBW) and small for gestational age (SGA) was lower. However, mean BW for Halland did not differ from the rest of Sweden in recent years 2004–2013. We also conducted a mortality follow-up for children born in Scania, which showed that LBW, being born SGA, or short birth length reduced survival. In conclusion, the high mean life expectancy in Halland compared to the rest of Sweden could have been associated with beneficial early life factors influencing birth size in the past. In more recent decades the mean BW of Halland is not different from the national mean. Thus, longevity could be expected to become more equal to the national mean in the future.