Pregnancy and risk of COVID‐19: a Norwegian registry‐linkage study

  1. MC Magnus
  2. L Oakley
  3. HK Gjessing
  4. O Stephansson
  5. HM Engjom
  6. F Macsali
  7. PB Juliusson
  8. A‐M Nybo Andersen
  9. SE Håberg

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Abstract

To compare the risk of acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) infection and contact with specialist healthcare services for coronavirus disease 2019 (COVID‐19) between pregnant and non‐pregnant women.

Population or sample

All women ages 15–45 living in Norway on 1 March 2020 ( n  = 1 033 699).

Methods

We linked information from the national birth, patient, communicable diseases and education databases using unique national identifiers.

Main outcome measure

We estimated hazard ratios (HR) among pregnant compared to non‐pregnant women of having a positive test for SARS‐CoV‐2, a diagnosis of COVID‐19 in specialist healthcare, or hospitalisation with COVID‐19 using Cox regression. Multivariable analyses adjusted for age, marital status, education, income, country of birth and underlying medical conditions.

Results

Pregnant women were not more likely to be tested for or to a have a positive SARS‐CoV‐2 test (adjusted HR 0.99; 95% CI 0.92–1.07). Pregnant women had higher risk of hospitalisation with COVID‐19 (HR 4.70, 95% CI 3.51–6.30) and any type of specialist care for COVID‐19 (HR 3.46, 95% CI 2.89–4.14). Pregnant women born outside Scandinavia were less likely to be tested, and at higher risk of a positive test (HR 2.37, 95% CI 2.51–8.87). Compared with pregnant Scandinavian‐born women, pregnant women with minority background had a higher risk of hospitalisation with COVID‐19 (HR 4.72, 95% CI 2.51–8.87).

Conclusion

Pregnant women were not more likely to be infected with SARS‐CoV‐2. Still, pregnant women with COVID‐19, especially those born outside of Scandinavia, were more likely to be hospitalised.

Tweetable abstract

Pregnant women are at increased risk of hospitalisation for COVID‐19.

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  1. Version published to 10.1111/1471-0528.16969
  2. ScreenIT

    SciScore for 10.1101/2021.03.22.21254090: (What is this?)

    Please note, not all rigor criteria are appropriate for all manuscripts.

    Table 1: Rigor

    Institutional Review Board StatementIRB: Ethical approval was obtained from the Regional Committee for Medical and Health Research Ethics of South/East Norway (# 141135).
    Randomizationnot detected.
    Blindingnot detected.
    Power Analysisnot detected.
    Sex as a biological variableStudy population and data sources: We followed all women between 15 and 45 years of age registered in the Norwegian National Population Registry on March 1st, 2020 (n= 1,033,699), until February 28th, 2021.

    Table 2: Resources

    Software and Algorithms
    SentencesResources
    All analyses were conducted in Stata version 16 (Statacorp, Texas).
    Statacorp
    suggested: None

    Results from OddPub: We did not detect open data. We also did not detect open code. Researchers are encouraged to share open data when possible (see Nature blog).

    Results from LimitationRecognizer: We detected the following sentences addressing limitations in the study:
    A limitation of registry studies is that health definitions rely on registrations from contact with healthcare. Test capacity for SARS-CoV-2 and healthcare availability for those with milder COVID-19 symptoms have varied through the pandemic. In the initial phase, testing was limited, and healthcare was restricted to those with more severe symptoms or underlying risk conditions. We found that pregnant women were slightly more likely to be tested in the initial phase than non-pregnant women, but after the initial months when testing capacity increased, pregnant women were slightly less likely to be tested. Asymptomatic women and women with milder symptoms were not captured and classified as infected in our data. However, results for the two waves of the pandemic in Norway yielded similar estimates, supporting that test-or healthcare availability was unlikely to explain our findings. Identifying ongoing pregnancies and early terminations through healthcare contacts is also prone to misclassification. Towards the end of the follow up period we were less likely to capture ongoing pregnancies that will end in miscarriage or induced abortions. Only 44.2% of miscarriages and induced abortions had a prior antenatal code. This could have resulted in underestimation of the number of pregnant women and attenuation of associations. Since antenatal visits are without information on gestational length information, we defined pregnancy start date and durations for ongoing pregnancies and ea...

    Results from TrialIdentifier: No clinical trial numbers were referenced.

    Results from Barzooka: We did not find any issues relating to the usage of bar graphs.

    Results from JetFighter: We did not find any issues relating to colormaps.

    Results from rtransparent:
    • Thank you for including a conflict of interest statement. Authors are encouraged to include this statement when submitting to a journal.
    • Thank you for including a funding statement. Authors are encouraged to include this statement when submitting to a journal.
    • No protocol registration statement was detected.

    About SciScore

    SciScore is an automated tool that is designed to assist expert reviewers by finding and presenting formulaic information scattered throughout a paper in a standard, easy to digest format. SciScore checks for the presence and correctness of RRIDs (research resource identifiers), and for rigor criteria such as sex and investigator blinding. For details on the theoretical underpinning of rigor criteria and the tools shown here, including references cited, please follow this link.

  3. Version published to 10.1101/2021.03.22.21254090v1 on medRxiv