Changes in the quantity and quality of births after the COVID-19 pandemic: an interrupted time series analysis of two million births in Southwest China

Whether the number and quality of births have been changed after the COVID-19 pandemic remains unclear. We aimed to examine whether the number of births, gestation weeks, and birth weight changed after COVID-19 in Chongqing, the largest municipality by area in China. Birth registration data of Chongqing from January 2015 to July 2022 were used to compare the quantity and quality (gestation week, preterm birth rate, birth weight, low birth weight rate) of births before and after the pandemic by interrupted time series analysis by autoregressive average moving models (ARIMA) and linear models of interrupted time series analysis (ITSA). October 2020, which was nine months after the onset of the first-wase of COVID-19 pandemic, was designated as the cut point to account for the gestation duration. Data from the Chongqing Preconception Reproductive Health and Birth Outcome Cohort were then utilized to analyze the temporal changes in pre-pregnancy body mass index (BMI) among reproductive-age women before (January 2019 to January 2020) and after the pandemic (March 2020 to March 2023). There were 2,099,898 birth records included. Before the pandemic, there were monthly declining trends in the number of births (β=-100.44, 95% CI: -181.82 to -14.06, P = 0.022) and gestation weeks (β=-4.7 × 10− 3, 95% CI: -6.3 × 10− 3weeks to -1.6 × 10− 3weeks, P < 0.001), and increasing trends in the rates of preterm births (β = 0.02%, 95% CI: 0.02% to 0.03%, P < 0.001) and low birth weight (β = 1.2 × 10− 2%, 95% CI: 8.9 × 10− 3% to 1.6 × 10− 2%, P < 0.001). Interrupted time-series analyses, after adjusting for seasonality and trend, showed that the declining trend in the number of births and gestation weeks did not change after COVID-19 (P = 0.428 and 0.492). Similarly, the upward trend in preterm birth rates did not change after COVID-19 (P = 0.135). However, the birth weight decreased faster after the pandemic, with an additional 1.48 g (95%CI: -2.81 g to -0.16 g, P = 0.028) per month compared to the pre-pandemic period. Similarly, the low birth weight rate increased at an accelerated pace after the pandemic, with an additional monthly increase of 0.03% (95%CI: 0.01% to 0.06%, P = 0.010) compared to the pre-pandemic period. Pre-pregnancy body mass index of reproductive-age women shifted from an increasing trend in the pre-epidemic period to a declining trend in the post-pandemic period (β=-0.05, 95%CI: -0.10 to -0.01, P = 0.039), in line with the accelerated decline of birth weight nine months later. The long-term trend of birth quality after the pandemic has changed and deserves attention.