Omicron in pregnancy: time to breathe easier?

COVID-19 has been concerning for pregnant women since the beginning of the pandemic, owing to the risk of severe maternal morbidity and the need for critical care in a population that is normally healthy.1

  • Wei SQ
  • Bilodeau-Bertrand M
  • Liu S
  • Auger N

The impact of COVID-19 on pregnancy outcomes: a systematic review and meta-analysis. However, the emergence of the omicron (B.1.1.529) variant might have marked a turning point for pregnant patients. Omicron is associated with less severe disease in many individuals, and possibly pregnant women as well.In The Lancet Respiratory Medicine, Sarah J Stock and colleagues examined maternal and infant outcomes during a delta (B.1.617.2)-dominant period and an omicron-dominant period.2

  • Stock SJ
  • Moore E
  • Calvert C
  • et al.

Pregnancy outcomes after SARS-CoV-2 infection in periods dominated by delta and omicron variants in Scotland: a population-based cohort study. Using data from a Scottish registry of pregnant women with COVID-19, the authors compared 4968 patients infected with SARS-CoV-2 during the omicron wave (from Dec 15, 2021, to Jan 31, 2022) with 4945 patients infected during the delta wave (from May 17 to Dec 14, 2021). Stock and colleagues assessed maternal admissions to critical care within 21 days of infection, as well as maternal death, preterm birth, stillbirth, low Apgar score, neonatal infection, and neonatal mortality within 28 days of maternal infection.

Their findings were reassuring. Compared with the delta variant, women with infections during the omicron-dominant period had a significantly lower risk of critical care admission (0·3% [13 of 4968] vs 1·8% [89 of 4955]; adjusted odds ratio 0·25, 95% CI 0·14–0·44) and preterm birth (1·8% [37 of 2048] vs 4·2% [98 of 2338]; 0·57, 0·38–0·87). Women with infections during the omicron-dominant period also appeared to have fewer stillbirths and neonatal deaths than those infected during the delta-dominant period. The results suggest that omicron might be less virulent in pregnancy, despite being more contagious than delta. Does this mean we can worry less about pregnant women at this stage in the pandemic? We highlight here three reasons to remain vigilant.

The first issue is whether vaccination contributed to decreased morbidity during the omicron wave. Stock and colleagues appropriately adjusted for vaccination. They also showed in sensitivity analyses of unvaccinated women that infections during the omicron-dominant period were associated with a persistently lower risk of critical care admission and preterm birth. However, associations in vaccinated women were not provided. COVID-19 vaccines are effective at reducing severe morbidity in pregnancy.3SARS-CoV-2 infection and COVID-19 vaccination in pregnancy. The authors should be able to show that infections during the omicron-dominant period at least led to fewer events in vaccinated women. Without this information, it is impossible to determine the added value of vaccination or protective effect overall. In an earlier study of the same Scottish dataset, Stock and colleagues showed that unvaccinated pregnant women were younger and more disadvantaged.4

  • Stock SJ
  • Carruthers J
  • Calvert C
  • et al.

SARS-CoV-2 infection and COVID-19 vaccination rates in pregnant women in Scotland. These characteristics affect the chance of infection and risk of severe morbidity and make the results from this group less generalisable. As more and more pregnant women become vaccinated, a more nuanced assessment of vaccination will be needed to determine the extent to which future variants are harmful.A second issue is the measurement of severe pregnancy morbidity, the key outcome when it comes to COVID-19. Stock and colleagues examined maternal critical care admission, preterm birth, stillbirth, neonatal death, and Apgar scores. However, these complications do not adequately capture severe maternal morbidity. Efforts to standardise the definition of severe maternal morbidity have progressed considerably in the past decade.5US Centers for Disease Control and Prevention
Severe maternal morbidity in the United States. Severe maternal morbidity includes concrete conditions such as respiratory failure, heart failure, and eclampsia.5US Centers for Disease Control and Prevention
Severe maternal morbidity in the United States.,  6

  • Mupanomunda M
  • Fakih MG
  • Miller C
  • et al.

Comparison of severe maternal morbidities associated with delivery during periods of circulation of specific SARS-CoV-2 variants. Although severe maternal morbidity frequently requires critical care, admission to an intensive care unit might occur for unrelated reasons.7

  • Godeberge C
  • Deneux-Tharaux C
  • Seco A
  • et al.

Maternal intensive care unit admission as an indicator of severe acute maternal morbidity: a population-based study. Some women might be admitted simply out of caution. Critical care admission cannot capture severe maternal morbidity in hospital centres that do not have intensive care units. Critical care, therefore, has uncertain value as an indicator of severe maternal morbidity.Currently, only one study considered the risk of severe maternal morbidity during the omicron wave.6

  • Mupanomunda M
  • Fakih MG
  • Miller C
  • et al.

Comparison of severe maternal morbidities associated with delivery during periods of circulation of specific SARS-CoV-2 variants. In an analysis of 15 633 pregnant women in the USA, omicron infection appeared to be associated with an increased risk of respiratory morbidity but not other types of severe maternal morbidity compared with no infection.6

  • Mupanomunda M
  • Fakih MG
  • Miller C
  • et al.

Comparison of severe maternal morbidities associated with delivery during periods of circulation of specific SARS-CoV-2 variants. However, the investigators could not account for vaccination. Stock and colleagues had vaccination data, but did not assess severe maternal morbidity, including respiratory complications that can be prevalent in pregnant women with COVID-19 infection. For now, we cannot know with certainty that omicron does not increase the risk of severe maternal morbidity.Third, Stock and colleagues analysed only patients with infection. They did not have an uninfected comparison group. The authors were able to show that infection with omicron is not as concerning as delta infection, but they did not provide risks relative to uninfected pregnancies. It would not be surprising to find that omicron continues to drive severe maternal respiratory morbidity, considering the known respiratory effect of SARS-CoV-2 and hospitalisation rates that have yet to return to normal.3SARS-CoV-2 infection and COVID-19 vaccination in pregnancy.,  6

  • Mupanomunda M
  • Fakih MG
  • Miller C
  • et al.

Comparison of severe maternal morbidities associated with delivery during periods of circulation of specific SARS-CoV-2 variants.,  8

  • Havers FP
  • Patel K
  • Whitaker M
  • et al.

Laboratory-confirmed COVID-19-associated hospitalizations among adults during SARS-CoV-2 omicron BA.2 variant predominance—COVID-19-Associated Hospitalization Surveillance Network, 14 States, June 20, 2021–May 31, 2022. An uninfected comparison group is essential to understand how much risk omicron continues to pose in pregnancy.

Stock and colleagues designed a much-needed study showing that the omicron variant is less risky to pregnant women than the delta variant. However, the bigger question of how much risk remains with the omicron variant has yet to be answered. To fill this gap, future research will need to pay careful attention to vaccination, relevant measures of severe maternal morbidity, and include an uninfected comparison group.

NA was funded by the Canadian Institutes of Health Research (PUU-177957) and Fonds de recherche du Québec-Santé (296785). The sponsors were not involved in the writing of the commentary nor in the decision to submit the commentary for publication. JH-P declares no competing interests.

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    Comparison of severe maternal morbidities associated with delivery during periods of circulation of specific SARS-CoV-2 variants.

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Article Info

Publication History

Published: October 07, 2022

Identification

DOI: https://doi.org/10.1016/S2213-2600(22)00390-3

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© 2022 Elsevier Ltd. All rights reserved.

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