The risk of maternal critical care admission and preterm birth were much lower amid dominance of the SARS-CoV-2 Omicron variant than during the Delta-dominant period, finds a Scottish study published late last week in The Lancet Respiratory Medicine.

A team led by University of Edinburgh researchers examined the maternal and pregnancy outcomes of 9,817 women with 9,823 pregnancies and 9,923 COVID-19 infections in a Scottish registry from May 17, 2021, to Jan 31, 2022. The study spanned the dominance of the Delta variant (May 17 to Dec 14, 2021) and Omicron (Dec 15, 2021, to Jan 31, 2022).

Fewer stillbirths amid Omicron

Each month of the Delta period, 1,710 to 2,658 per 100,000 pregnant women were infected, while the infection rate during Omicron was 11,011 per 100,000.

Relative to Delta cases, Omicron infections were tied to a lower risk of maternal critical care admission within 21 days of infection (0.3% of 4,968 vs 1.8% of 4,955; adjusted odds ratio [aOR], 0.25) and preterm birth within 28 days (1.8% vs 4.2%; aOR, 0.57). There were no maternal deaths within 28 days.

Estimates of low Apgar scores (indicating need for special neonatal care) lacked precision because of low numbers, at 11 (2.1%) of 528 with Delta and 5 (1.2%) of 423 with Omicron. Lower rates of stillbirths occurred during Omicron than during Delta (2 of 462 [4.3 per 1,000] births vs 13/639 [20.3 per 1,000]). Twelve of the 15 stillbirths occurred in women who had not received at least two doses of COVID-19 vaccine before their infections.

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