Objective: To investigate the trend in preterm birth (PTB) rates and the influence of several potential maternal risk factors on PTB in Italy from January 2018 to December 2022, before and after COVID-19 pandemic. Design: Population-based study covering 86.11% of all Italian births. Methods: We conducted an interrupted time series analysis to examine the PTB trend. Using Poisson regressions, we assessed the associations (risk ratio, RR) of potential risk factors with PTB and calculated their population impact fractions (PIFs). Main outcome measures: Primary outcomes included the temporal trends of PTB rates before and after the pandemic, and the change during the pandemic. Secondary outcomes involved the associations of potential risk factors with PTB rates, and PIFs. Results: We observed a monthly decrease in PTB rate until July 2020 [-0.2% (95% CI: -0.3; -0.1)], followed by an interruption with an abrupt drop of -5% in July 2020 (95% CI: -7.3; -2.7). From August 2020 until December 2022 the trend remained flat (-0.02%, 95% CI: -0.5; 0.5). Among studied risk factors, low maternal education, unemployment and foreign nationality were associated with PTB [RR: 1.14 (95% CI: 1.04;1.24), 1.08 (1.05;1.12), and 1.17 (1.14;1.21), respectively], and showed a decreasing trend after pandemics; the impact (PIFs) on PTB rates was modest with a decrease between 2.4 and 4.2‰ PTB. Conclusions: We confirmed a decrease in PTB rates before and during the pandemic described also in other European countries. In Italy, post-pandemic PTB trend remained flat. Socioeconomic risk factors for PTB only marginally explained this pattern. Tweetable abstract In Italy, the decrease in preterm births before and during COVID-19 stopped after the pandemic; the impact of socio-economic disparities was minimal