The Impact of the COVID-19 Pandemic on the Sex Ratio at Birth in Ireland.

Objectives: The sex ratio at birth (SRB), calculated as male divided by total live births, is an important indicator of population health. Typically, male live births slightly outnumber female live births. Population events, including pandemics, can alter the SRB, with effects sometimes evident 9 months post-event, potentially due to changes in sexual behavior and/or stress levels. This study investigates the impact of the COVID-19 pandemic on the SRB in the Republic of Ireland.

Methods: Publicly available monthly live birth data for Ireland were obtained from the Central Statistics Office for the period 2015 to 2021. Time series analysis predicted the SRB for 2020 using data from 2015 to 2019, with comparisons made between observed and predicted values.

Results: In December 2020, 9 months after the March 2020 COVID-19 declaration, the observed SRB sharply fell to 49.44% (97.80 males for every 100 females), below the 95% prediction interval of 50.31% to 52.15%, significantly deviating from the expected male predominance. December 2020 also recorded the lowest average daily number of births (n = 145) in the study period.

Conclusion: The sharp decline in the SRB in December 2020, alongside the lowest birth count, suggests reduced sexual intercourse at the population level, particularly in March 2020, aligning with recommendations from Ireland's Health Service Executive (HSE). The HSE advocated precautionary measures such as limiting partnered sex in March 2020 to mitigate the spread of COVID-19. These findings highlight the pandemic's potential impact on population dynamics and stress the importance of SRB monitoring as a low-cost and readily available health indicator, especially during national crises.