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Pregnancy outcomes following Delta and Omicron SARS-CoV-2 infection in Scotland

October 2022: Research published in The Lancet Respiratory Medicine looks at the impact of COVID-19 on the health of pregnant women, and their babies, after Delta and Omicron infections.

Pregnancy outcomes following Delta and Omicron SARS-CoV-2 infection in Scotland:a population-based cohort study

Stock, SJ; Moore, E.K; Calvert, C; Carruthers, J; et. al

The Lancet Respiratory Medicine

Published online one: 7 October 2022

Available online at: https://doi.org/10.1016/S2213-2600(22)00360-5

Summary in plain English

Having an infection like coronavirus (SARS-CoV-2) can impact the health of a pregnant woman and her baby. The SARS-CoV-2 virus causes COVID-19 disease.

There are different variants of SARS-CoV-2 which can cause different symptoms. Two major waves of infection in the UK were caused by the Delta and Omicron variants:

  • Delta (B.1.617.2): Most common variant in Scotland from 17 May to 14 December 2021;
  • Omicron (B.1.1.529): Most common variant in Scotland from 15 December 2021.

Why did we carry out this research?

Having COVID-19 while pregnant is linked to a higher risk of serious pregnancy complications. This includes:

  • Maternal critical care: A pregnant woman who is admitted to an intensive care unit (ICU) or high-dependency unit (HDU).
  • Premature birth: A baby that is born alive more than three weeks before the due date.
  • Stillbirth: A baby that is born dead after 20+ weeks of pregnancy.

Some studies have shown that the Delta variant causes more severe complications during pregnancy than previous variants. These may need hospital treatment. However, there is very little data about the effect of the Omicron variant during pregnancy on the health of women and their babies.

We wanted to understand the risk that Omicron infections pose to pregnancy health. This includes comparing the risk of maternal critical care, premature birth, stillbirth and neonatal death following Omicron and Delta infections.

What data did we use?

To carry out this study, we looked at health data in the ‘COVID-19 in Pregnancy in Scotland Study’ (COPS) database. This database is updated to include all women aged 11-55 who were known to be pregnant in Scotland between 1 January 2015 and the present day.

Find out more about COPS data

We looked at complications shortly after an infection during pregnancy.

To do this, we analysed data for women in COPS who had a SARS-CoV-2 infection between 17 May 2021 and 31 January 2022. Our results took account of each person’s age, ethnicity, stage of pregnancy, vaccine status, and whether they live in a deprived area.

What did we find?

SARS-CoV-2 infections

We found the following number of infections during pregnancy in our study:

  • 4955 infections in the Delta period (17 May to 14 December 2021)
  • 4968 infections in the Omicron period (15 December 2021 to the end of our study period on 31 January 2022).

Maternal critical care and death

There were no maternal deaths within 28 days of a positive test during the study.

We found fewer admissions to critical care among women infected in the Omicron period (0.3% pregnancies) than in the Delta period (1.8% pregnancies). COVID-19-specific critical care rates were also lower during the Omicron period.

Premature births, stillbirths and neonatal infections and deaths

There were fewer preterm births during the Omicron period (1.8% pregnancies) compared to Delta (4.2% pregnancies). This was for women who were infected between 20 and 36 weeks of pregnancy.

We also found that stillbirths, neonatal infection and neonatal deaths all went down during the Omicron period:

  • Delta: 20.3 stillbirths, 17.6 infections and 6.3 neonatal deaths per 1000 births;
  • Omicron: 4.3 stillbirths, 2.1 infections and 0 neonatal deaths per 1000 births.

Why is this research important?

This study is the first of its kind to compare COVID-19 risk to pregnant women and their babies during the Delta and Omicron waves of the pandemic. It uses health data from the whole of the Scottish population.

Overall it suggests that, as with non-pregnant adults, the Omicron variant B.1.1.529 is not as strongly linked with COVID-19 pregnancy complications as the Delta variant.

Understanding the impact of new variants on pregnancy is crucial for making evidence-based public health and maternity care policies.


This plain English summary was written by our Patient and Public Involvement Lead Lana Woolford, with the support and feedback of the EAVE II Public Advisory Group (PAG) and researchers. This particular summary was reviewed by PAG members Hameed K and JC.

This research was done as part of the EAVE II associated project COPS (COVID-19 in Pregnancy in Scotland).

Click here to visit the COPS website