Background: We aimed to assess and compare short-term pregnancy outcomes following SARS- CoV-2 Delta (B.1.617.2) and Omicron (B.1.1.529) variant infection in pregnancy.

Methods: We conducted a national population-based cohort study of women who had SARS-CoV-2 in pregnancy between May 17, 2021 and January 31, 2022. Outcomes were any maternal critical care admission within 21 days of infection and maternal critical care admission for COVID-19; and preterm birth (<37 weeks' gestation); stillbirth; neonatal death and low Apgar score (<7/10; term births only) in births within 28 days of infection. We used time periods when variants were dominant in the general Scottish population, based on ≥50% cases being S gene-positive (Delta; May 17 - December 14, 2021) or negative (Omicron; December 15, 2021 - January 31, 2022) as surrogates for variant infections. Analyses used logistic regression, adjusting for maternal age, deprivation, ethnicity, gestation and vaccination status. Sensitivity analyses included restricting to those with first confirmed SARS-CoV-2 infection; use of time periods where Delta and Omicron were ≥90% dominant; and restricting to those who were unvaccinated at the time of infection; and including pre-existing clinical vulnerability and smoking status.

Findings: Compared to infections in the Delta period, SARS-CoV-2 infections in pregnancy in the Omicron period were associated with lower maternal critical care admission risk (0·3% versus 1·8%; adjusted Odds Ratio [aOR] 0·25, 95% Confidence Interval [CI] 0·14-0·44) and preterm birth within 28 days of infection at 20+0 to 36+6 weeks gestation (1·8% versus 4·2%; aOR 0·57; 95% CI 0·38-0·87). There was imprecision around estimates of low Apgar scores due to low numbers (aOR Omicron vs Delta 0·72 95% CI 0·23-2·32). There were fewer stillbirths in the Omicron period vs Delta (4·3 (2/462) per 1000 births versus 20·3 (13/639) per 1000) and no neonatal deaths during Omicron (0/460; 0 per 1000 versus 4/626; 6·3 per 1000]) so numbers were too small to support adjusted analyses. Findings in sensitivity analyses were similar to main analyses.

Interpretation: Pregnant women infected with SARSCoV-2 were substantially less likely to have a preterm birth or maternal critical care admission during the Omicron period than during the Delta period.

Funding: Wellcome Trust, Tommy’s charity, Medical Research Council, UK Research and Innovation, Health Data Research UK, National Core Studies – Data and Connectivity, Public Health Scotland, Scottish Government DG Health and Social Care, Scottish Government Chief Scientist Office, National Research Scotland.

Cite as

Stock, S., Moore, E., Calvert, C., Carruthers, J., Denny, C., Donaghy, J., Hillman, S., Hopcroft, L., Hopkins, L., Goulding, A., Lindsay, L., McLaughlin, T., Taylor, B., Auyeung, B., Katikireddi, S., McCowan, C., Ritchie, L., Rudan, I., Simpson, C., Robertson, C., Sheikh, A. & Wood, R. 2022, 'Pregnancy outcomes following SARS-CoV-2 infection in Delta and Omicron dominant periods in Scotland: A population-based cohort study', The Lancet Respiratory Medicine. https://doi.org/10.1016/S2213-2600(22)00360-5

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Last updated: 03 May 2024
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