Sex-specific Infant Mortality Trends in Switzerland (1950 - 2022) and Test of the Null Hypotheses of No Trend Changes after the Chernobyl Accident in 1986

Abstract

Background: In Switzerland after the Chernobyl accident in April 1986, the cumulative radiation dose up to 2005 was around 3,500 Sieverts, corresponding to 25 µSv/year per person. Stillbirths, perinatal mortality, and congenital malformations increased in a dose-dependent and sex-specific manner in numerous countries affected by Chernobyl fallout. Less attention has been paid to the gender specific infant mortality rate. The aim of this report is to study the secular sex-specific infant mortality trends in Switzerland (1950 - 2022) and to test the null hypotheses of no trend changes after the Chernobyl accident in 1986.

Methods: Counts of annual live births (LB) and infant deaths (ID) under 1-year of age by gender for Switzerland from 1950 to 2022 were obtained from the human mortality database. Time trend analyses of total, female, and male ID proportions employing logistic regression were carried out. Possible level-shifts in the annual mortality rates and in the ID vs LB sex odds ratios (SOR) from 1987 onward were estimated and tested.

Results: The overall ID proportion in the period 1950 - 2022 was 1.13% (female 0.99%, male 1.27%), i.e., 69,905 total ID in 6,186,134 total LB (female 29,677 vs 3,010,130 and male 40,228 vs 3,176,004). In Switzerland, total female and male infant mortality rates abruptly increased in 1987 relative to the monotone secular downward trends as estimated from the period 1950 - 1986. The jump OR in 1987 with 95% confidence interval and p value for the total (female + male) mortality was 1.175 (1.102, 1.253) p value < 0.0001; females: 1.187 (1.095, 1.287) p value < 0.0001; males 1.167 (1.078, 1.262) p value 0.0001. The relatively stable infant mortality SOR in the period 1950 to 1986 of 1.307 (1.283, 1.331) decreased continuously in the period after 1986 to a value of 1.134 in 2022, according to a 10-year sex period interaction OR of 0.960 (0.939, 0.982) p value 0.0003.

Conclusion: The jumps in the infant mortality rates in Switzerland in 1987 and the changing annual infant Mortality vs LB SOR during the post-Chernobyl period indicate possible sex-differential radio contamination impacts and corroborate previous findings of increased sex-linked detrimental radiation induced genetic effects after Chernobyl.