The impact of mitigation measures on perinatal outcomes during the first nine months of the COVID-19 pandemic: a systematic review with meta-analysis

Worldwide reports have produced conflicting data on perinatal outcomes during the COVID-19 pandemic. This systematic review and meta-analysis addressed the effect of mitigation measures against COVID-19 on preterm birth, stillbirth, low birth weight, and NICU admission during the first nine months of the pandemic. A search was performed using MEDLINE, Embase and SCOPUS for manuscripts published up until 24th May 2021. Studies that reported perinatal outcomes (preterm birth, stillbirth, low birth weight, NICU admission) during the COVID-19 pandemic with a pre-pandemic control period were included. Risk of bias assessment was performed using ROBINS-I tool. RevMan5 was used to perform meta-analysis with random-effects models. A score of the stringency of mitigation measures was calculated from the Oxford COVID-19 Government Response Tracker. Thirty-eight studies of moderate to serious risk of bias were included, with varied methodology, analysis and regional mitigation measures, using stringency index scores. There was no overall effect on preterm birth at less than 37 weeks (OR 0.96, 95% CI 0.92- 1.00). However, there was a reduction in preterm birth at less than 37 weeks (OR 0.89, 95% CI 0.81-0.98) and 34 weeks (OR 0.56, 95% CI 0.37-0.83) for iatrogenic births and in singleton pregnancies. There was also a significant reduction in preterm births at less than 34 weeks in studies with above median stringency index scores (OR 0.71, 95% CI 0.58-0.88). There was no effect on risk of stillbirth (OR 1.04, 95% CI 0.90-1.19) or birth weight. NICU admission rates were significantly reduced in studies with above median stringency index scores (OR 0.87, 95% CI 0.78-0.97). The reduction in preterm births in regions with high mitigation measures against SARS-CoV-2 infection is likely driven by a reduction in iatrogenic births. Variability in study design and cohort characteristics need to be considered for future studies to allow further investigation of population level health measures of perinatal outcomes.