Impact of the COVID-19 pandemic on small vulnerable newborns: an interrupted time series analysis in Peru and Brazil.

Background: We examined COVID-19's impact on the number of small vulnerable newborns (SVN) at national and regional levels in Peru and Brazil. Methods: Using national birth registries, we examined monthly numbers of preterm (PT), low birthweight (LBW), and small for gestational age (SGA) newborns. We analysed COVID-19's impact on SVN using two interrupted time series models. We estimated SVN's expected numbers in the absence of the pandemic using mixed-effects regressions and calculated percent changes by comparing these estimates to observed during the pandemic. Incidence rate ratios (IRR) were estimated using Poisson regression. Results: In Peru, the average percent changes in PT, LBW, and SGA births were -17%, -11%, and -3% in 2020, and -10%, -4%, and +2% in 2021, respectively. The IRR of PT and LBW declined throughout the pandemic, while SGA IRR increased in August 2020-November 2020 and May 2021-December 2021. The Coast region experienced the greatest drop in PT, LBW, and SGA IRR in 2020, followed by a slight increase in 2021, whereas the Highlands and Amazon regions had increased LBW and SGA IRR. In Brazil, the percent changes in PT, LBW, and SGA births were +1%, -3%, and -8% in 2020, and +1%, 0%, and -1% in 2021, respectively. Most PT, LBW, and SGA IRRs decreased during the pandemic, except in the Northeast and Southeast regions, where PT increased in 2020. All regions experienced declines in LBW and SGA in 2020, with the Central-West and South regions showing the greatest LBW declines and Central-West region the highest SGA decrease. Conclusions: No significant worsening of neonatal outcomes were observed during the COVID-19 pandemic. In Peru, PT and LBW births declined, while SGA increased from August 2020. In Brazil, PT births slightly increased, while LBW and SGA births declined in 2020, remaining stable in 2021.