P2C247: COVID-19 Lockdown Related to Decrease of Premature Birth Rate and Increase of Birth Weight in Metropolitan France

Background: Preterm birth (PTB) is one of the leading causes of perinatal morbidity and mortality. The worldwide rate has been increasing in the last 2 decades in most developed countries. PTB is at the crossroads of genetic, epigenetic, biological, behavioral and environmental factors. The COVID-19 pandemic lockdown has provided a unique opportunity to assess the effects of socio environmental and lifestyle factors on PTB rate and on birthweight.

Methods: This national retrospective observational study evaluated the evolution of the rate of PTB and birthweight in the whole metropolitan France from January 2016 to December 2020. Global PTB and the different sub-categories of PTB were tested separately. We studied the birth weight before and after lockdown for all live births, for term and premature neonates and stratified analyses for low, very low (VLBW) and extremely low birth weight (ELBW). Each comparison was based on similar months of previous years to avoid bias due to seasonal variations.

Results: Data from 2,949,372 births from January 2016 to December 2019 including 228,857 PTB were compared to those of 699,344 births from January to December 2020 and 51,886 PTB. The national rate of PTB from march to december decreased significantly from 7.7% to 7.3%. The decrease was observable early from the 2 first months of lockdown and was persistent up to nine months after. This decrease was observed only for moderate PTB (March-July, RR = 0,997 [0,998 – 0,996]), whereas the very PTB and extremely PTB remain stable at that time. The national mean birth weight for full term babies increased after the lockdown (+0,16%, p< 0,0001). This increasing was detectable two months after the start of the lockdown (+0,11%; p=0,003) and was observable up to 8 months later. The proportion of children with LBW also varied after the lockdown with a decreased prevalence 2 months after the lockdown (-0,15%; p=0,02). For VLBW, the difference only appeared over the 6 months post lockdown period (-0,06%; p=0,006). For ELBW, there was no difference between the lockdown period and previous years.

Conclusion: Overall this nationwide study shows a significant reduction of prematurity and a significant increase of birth weight in France after lockdown for a period of time not limited to the lockdown itself. The COVID-19 lockdown imposed radical changes in lifestyle behaviors (physical activities, diet, exposure to air pollution, remote working) and it remains difficult to determine which factor played a role. A more in-depth study of factors determining these variations should drive prematurity prevention policy.