The role of parental composition in improved birth outcomes during the COVID-19 pandemic in Finland

BACKGROUND: In some high-income contexts, the COVID-19 pandemic was associated with improved birth outcomes, which was hypothesised to be caused by a positive effect of the pandemic on maternal health. Conversely, an improvement in birth outcomes may have been driven by pandemic-induced compositional changes in parental characteristics, which are associated with health outcomes at birth. Research on this consequence of the COVID-19 pandemic is critical for understanding pandemic-induced changes in population health (inequalities) and planning of public service provision. METHODS: We analysed population-wide data on birth outcomes and parental sociodemographic characteristics from Finland collected between January 2015 and December 2021 (n = 336,000). The total effect of pandemic-induced compositional changes on birth weight and preterm birth rate was estimated by segmented regression models using three conception cohorts: a) conceived prior to May 2019, b) conceived between June 2019 and February 2020 (to account for in-utero exposure to the pandemic), and c) conceived during the pandemic between March 2020 and February 2021 (to prevent selection bias). PRELIMINARY RESULTS: Adjusting for secular trends and seasonality, and accounting for in-utero exposure to the pandemic, the estimated effect of parental compositional change on average birth weight was 36.5 grams [95%CI: 24.8; 48.3]. Correspondingly, this compositional change was associated with a 16.2% [95%CI: 8.8%; 23%] lower risk of preterm birth for babies conceived during the pandemic. CONCLUSIONS: Pandemic-induced changes in parental composition drove the modest increase in birth weight and substantial reduction in preterm births for babies conceived during the pandemic. Should the postponed pregnancies among population groups at risk for worse birth outcomes eventually realise post-COVID-19, health care and educational systems may need to prepare for cohort-specific variations in service demand. KEY MESSAGES: • Improvement in birth weight and preterm birth rate among babies conceived during the COVID-19 pandemic were driven by pandemic-induced changes in parental composition. • Further research using natural experimental designs on this compositional change and health outcomes can inform future public service provision.