Introduction
Soon after the onset of the COVID-19 pandemic, several reports showed an increased risk of severe illness in pregnant women with SARS-CoV-2 compared with those non-pregnant, and adverse pregnancy outcomes including preterm birth.1 On the other hand, a more recent Italian study showed that most infected pregnant women and newborns had good outcomes.2 Recently, the Euro-Peristat Research Network3 raised concern about the fact that one major gap in assessing the real effects of the pandemic on maternal and child health was the limited availability of comprehensive population-based routine data.
Research has also accumulated on the effects of the pandemic on the general population of pregnant women and their infants, possibly due to mitigation strategies and changes in women everyday life. During the early months of the pandemic, a reduced preterm birth (PTB) rate, in comparison with that in the previous years, was recorded in Denmark,4 in one hospital in Ireland,5 and in one Italian Region,6 where also an increase in stillbirths was observed. Another study, performed in a single hospital in London, reported only an increase in stillbirths but not in PTB rates.7 These reports were based on relatively small samples, and limited, especially for stillbirths, also by a possible change in referral patterns of pregnant women.
A first systematic review and meta-analysis of 31 studies published until January 8th 2021 addressing the indirect effects of the pandemic on perinatal outcomes confirmed a slight reduction in PTB (< 37 weeks gestational age, GA) in high-income but not in low-income countries and, vice versa, an increase in stillbirths in low-income countries only.8
A more recent systematic review and meta-analysis of 44 studies9 found that the odds of PTB during the pandemic period were significantly reduced in single-centre/single-health-authority studies, while there was no difference in larger studies based on regional/national data. No difference was documented in the rate of stillbirths in the pandemic period compared to the non-pandemic one, though these conclusions might be hampered, according to the authors, by more limited data. The review once again concludes that there is still a need of studies in bigger countries largely affected by COVID-19 pandemic like India, Brazil, UK and Italy and based on national registries, to investigate the impact of the pandemic on perinatal health at a population level.
The aim of the present study was to provide national population-based estimates of the PTB and stillbirth rates during the pandemic period compared to a historical period. In order to account for the natural variation in PTB over time, and the abrupt implementation of public health measures and disruption of routines of care, we also analysed the temporal trend in monthly incidence of PTB before and after the implementation of mitigation measures.