Impact of COVID-19 mitigation measures on the incidence of preterm birth by time window
| Preterm birth | +1 month (n=11 360) | +2 months (n=24 196) | +3 months (n=36 319) | +4 months (n=48 812) | +5 months (n=61 591) | 7th–12th month (n=85 845) |
| Preterm birth | 0.83 (0.67 to 1.04) | 0.80 (0.69 to 0.94) | 0.83 (0.73 to 0.94) | 0.82 (0.73 to 0.92) | 0.84 (0.76 to 0.93) | 1.02 (0.94 to 1.11) |
| 32 complete weeks to 36 weeks and 6 days | 0.85 (0.68 to 1.08) | 0.86 (0.73 to 1.00) | 0.84 (0.73 to 0.96) | 0.83 (0.74 to 0.94) | 0.86 (0.77 to 0.97) | 1.09 (0.99 to 1.19) |
| <32 complete weeks | 0.69 (0.35 to 1.35) | 0.65 (0.40 to 1.05) | 0.90 (0.63 to 1.27) | 0.87 (0.65 to 1.17) | 0.81 (0.62 to 1.06) | 0.63 (0.47 to 0.83) |
| Stillbirth | / | / | 0.64 (0.29 to 1.40) | 0.82 (0.45 to 1.51) | 0.83 (0.48 to 1.43) | 0.92 (0.57 to 1.47) |
ORs (95% CI) indicating odds of preterm birth and stillbirth across various time windows (month) directly following implementation of the COVID-19 lockdown measures versus the odds of preterm birth and stillbirth in same time windows preceding the measures (2014–2019). ORs were adjusted for maternal age, insurance status, BMI at first prenatal visit, education level, type of conception, medical and obstetric complications.
BMI, body mass index.