BACKGROUND: The Icelandic volcano Laki erupted from June 1783 through January 1784. It produced 122 megatons of sulfur dioxide, particulate matter, and acid rain and contributed to one of the coldest winters on record in Western Europe. Although uncontrollable volcanic eruptions continue, few studies have investigated their perinatal health implications. METHODS: Using the Human Mortality Database, we assessed the association between the Laki event and the secondary sex ratio, infant mortality rates, and the number of births from 1751 to 1800 with time-series models that controlled for temporal trends. RESULTS: The secondary sex ratio decreased 3% below expected levels in 1784 (95% CI = -4%, -1%). Both female and male infant mortality rates exceeded expectation in 1785, by 54% (95% CI = 25%, 83%) and 37% (-1%, 74%), respectively. We observed little change in female live births but a reduction in male live births in 1784. CONCLUSIONS: Our findings are consistent with the hypothesis that the large-scale Laki volcanic eruptions of 1783-1784 resulted in adverse perinatal health outcomes in Sweden.
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