Preterm birth after the introduction of COVID-19 mitigation measures in Norway, Sweden, and Denmark: a registry-based difference-in-differences study

Abstract

Background Although some studies have reported a decrease in preterm birth following the start of the COVID-19 pandemic, the findings are inconsistent. Objective This study aimed to compare the incidences of preterm birth before and after the introduction of COVID-19 mitigation measures in Scandinavian countries using robust population-based registry data. Study Design This was a registry-based difference-in-differences study using births from January 2014 through December 2020 in Norway, Sweden, and Denmark. The changes in the preterm birth (<37 weeks) rates before and after the introduction of COVID-19 mitigation measures (set to March 12, 2020) were compared with the changes in preterm birth before and after March 12 from 2014 to 2019. The differences per 1000 births were calculated for 2-, 4-, 8-, 12-, and 16-week intervals before and after March 12. The secondary analyses included medically indicated preterm birth, spontaneous preterm birth, and very preterm (<32 weeks) birth. Results A total of 1,519,521 births were included in this study. During the study period, 5.6% of the births were preterm in Norway and Sweden, and 5.7% were preterm in Denmark. There was a seasonal variation in the incidence of preterm birth, with the highest incidence during winter. In all the 3 countries, there was a slight overall decline in preterm births from 2014 to 2020. There was no consistent evidence of a change in the preterm birth rates following the introduction of COVID-19 mitigation measures, with difference-in-differences estimates ranging from 3.7 per 1000 births (95% confidence interval, −3.8 to 11.1) for the first 2 weeks after March 12, 2020, to −1.8 per 1000 births (95% confidence interval, −4.6 to 1.1) in the 16 weeks after March 12, 2020. Similarly, there was no evidence of an impact on medically indicated preterm birth, spontaneous preterm birth, or very preterm birth. Conclusion Using high-quality national data on births in 3 Scandinavian countries, each of which implemented different approaches to address the pandemic, there was no evidence of a decline in preterm births following the introduction of COVID-19 mitigation measures.

Preterm birth rates were slightly lower in Denmark during the first year of the COVID‐19 pandemic compared with the previous 4 years

“…A study that included population‐based data on live births and stillbirths in Norway, Sweden and Denmark has also been published. 16 This registry‐based study used the difference‐in‐differences method to analyse births from January 2014 to December 2020, before and after the introduction of COVID‐19 restrictions. The data were analysed for the 2 weeks before 12 March 2020, and the day after a global pandemic was declared, and 16 weeks after that date.…”

Limited Effects of SARS-CoV-2 Pandemic-related Lockdowns and Reduced Population Mobility on Preterm Birth Rates: A Secondary Analysis of Bavarian Obstetric Quality Parameters from 2010 to 2020

“…So far, only one study has investigated potential long-term trends. That study summarized centrally reported data from Norway, Sweden and Denmark 22 . The results of that study and our work are congruent.…”

Preterm birth rates among twins during the Danish COVID-19 lockdown and mitigation period

“…mobility patterns, and psychological responses to these, varied considerably between countries and over time 1 . The COVID-19 lockdown constitutes an important quasi-experiment with respect to identification of novel methods to prevent preterm birth (PTB) 3 .…”

“…Three subsequent studies, which included Danish data, all examined PTB rates without excluding multifetal pregnancies 3-5 . This makes data interpretation difficult, as multifetal pregnancies have a different set of risk factors for PTB, increased risk of adverse outcome, and a shorter expected pregnancy length.…”

“…As an illustration of the impact of combining multifetal with singleton births, a study based on data from several international Neonatal Intensive Care Units (NICUs) reported a decrease in NICU admissions of xPTBs, including multifetal births, in Denmark and Norway of 18 % during the most restrictive three-month mitigation period 4 . If it is accepted that Norway did not experience a reduction in xPTBs 3 , assuming a 10 % proportion of multifetal xPTB pregnancies, then the Danish reduction of singleton xPTBs pregnancies over a three-month period can be estimated to be ~ 40 %. Clearly compatible with the 73 % (95% CI, 14 % - 93 %) reduction in xPTBs found in the Danish National Patient Register based study on all Danish singleton preterm births 1 , and the 56 % and 47 % reductions in xPTBs in March and April 2020 reported in a study based on data from the Danish Newborn Quality Database 5 .…”