Trends in Preterm Births in Italy and Maternal Risk Factors in 2018–2022—A Registry-Based Study

Background: Nationwide studies described a reduction in preterm birth (PTB) during the Coronavirus disease 19 (COVID-19) pandemic, but this was not confirmed in others. Very few data are available on the trend of PTBs over a longer period, including the post-pandemic period, and on potential risk factors, especially those associated with social disparities. Objective: To investigate the trend in PTB rates and the influence of maternal risk factors in Italy from January 2018 to December 2022, based on 12 Regional Birth Registries covering 86.1% of Italian births. Methods: PTB trend was investigated by an interrupted time series analysis. We assessed the associations of potential risk factors with PTB (Poisson regressions) and calculated their population impact fractions (PIFs). Results: We studied 1,762,422 births; 7.25% were PTB. Before the pandemic, we observed a monthly decrease in PTB rate [−0.2% (95% CI: −0.3; −0.1)]; from July 2020 onwards, the average monthly level of PTBs was 5% lower than before (95% CI: −7.3; −2.7), with a flat trend until December 2022 [−0.02% (95% CI: −0.5; 0.5)]. Socio-economic maternal risk factors (low education, unemployment) and foreign nationality, whose risk ratios were 1.14 (95% CI: 1.04; 1.24), 1.08 (1.05; 1.12), and 1.17 (1.14; 1.21), respectively, showed a decreasing trend after pandemic; their impact on the decrease in PTBs was modest (PIFs between −2.4‰ and −4.2‰). Conclusions: The COVID-19 pandemic changed the pattern of PTB rates in Italy, lowering their average frequency and interrupting a previous decreasing trend. Changes in the trend of socio-economic maternal risk factors marginally explained this pattern.