SARS-CoV-2 and the role of vertical transmission from infected pregnant women to their fetuses: systematic review.

  1. Annette Pluddemann
  2. Elizabeth A Spencer
  3. Carl Heneghan
  4. Jon Brassey
  5. Igho J Onakpoya
  6. Elena Cecilia Rosca
  7. David H Evans
  8. John M Conly
  9. Tom Jefferson

Reviewed by

Read the full article See related articles

Listed in

Log in to save this article

Abstract

Background Vertical transmission of SARS-CoV-2 has been reported but does not appear to be common. This study aims to systematically review the evidence for vertical transmission of SARS-CoV-2. Methods This review is part of an Open Evidence Review on the transmission dynamics of SARS-CoV-2 and the role of intrauterine mother to fetus transmission. Literature searches were performed in the WHO Covid-19 Database, LitCovid, medRxiv, and Google Scholar for SARS-CoV-2 using keywords and associated synonyms, search date up to 20 December 2020, no language restrictions. Results We included 106 studies assessing vertical transmission of SARS-CoV-2 from pregnant women to their neonates: these studies comprised 40 reviews (21 fulfilled systematic review methodology, including risk of bias assessment of included studies) and 66 primary studies including 32 case reports (of up to two cases) and 34 prospective and retrospective cohort studies, prospective and retrospective case series, observational studies (including asymptomatic screening), database studies and a quality improvement project. Almost all were conducted in a hospital setting. The 32 case reports were considered to be at high risk of bias, due to the study design; across the 34 remaining primary studies, risk of bias was low to moderate. Sixteen case reports examined vertical transmission, which was not related to maternal symptomatology. For the cohort and case series studies, the percentage of positive neonates ranged from 0% to 22% across the studies. Twenty studies reported no positive vertical transmission. Three studies that reported the highest positivity rates of 11%, 15% and 22% had specifically selected neonates with a positive test (within up to 35 days) within the study population and were therefore more selective populations. Across the cohort and case series studies there were 65/2391 (2.7%) neonates born to mothers with a diagnosis of COVID-19 tested positive for SARS-CoV-2 within 24 hours of birth. No evidence correlated maternal symptomatology to vertical transmission. Mode of delivery did not correlate with rates of vertical transmission. Of 25 studies, 7 identified SARS-CoV-2 in placental tissue; some of these did not demonstrate vertical transmission to the neonate. No study reported the results of viral culture to detect SARS-CoV-2. Conclusions The results of these studies indicate that vertical transmission is possible, but is not frequent, and factors that influence when vertical transmission occurs are unknown. Further studies using standardised methods to establish viral infection are needed to establish vertical transmission rates and to assess clinical and other conditions affecting transmission.

Article activity feed

  1. ScreenIT

    SciScore for 10.1101/2021.06.30.21259750: (What is this?)

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

    Table 1: Rigor

    Ethicsnot detected.
    Sex as a biological variablenot detected.
    Randomizationnot detected.
    Blindingnot detected.
    Power Analysisnot detected.

    Table 2: Resources

    Software and Algorithms
    SentencesResources
    We are conducting an ongoing literature search in the WHO Covid-19 Database, LitCovid, medRxiv, and Google Scholar for SARS-CoV-2 for keywords and associated synonyms.
    Google Scholar
    suggested: (Google Scholar, RRID:SCR_008878)

    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:
    Strengths and limitations of the study: We conducted a comprehensive search of the literature on vertical transmission of SARS-CoV-2, also including studies that had not yet undergone peer review. We also accounted for the reporting quality of included primary studies. However, we may have missed some relevant studies and recognise that several studies may have been published after December 2020, which was the end date for the search. For example, there may now be more high quality cohort studies as much of the early evidence, as identified in this review, constituted single case studies. The aim of this review was to assess the evidence for vertical transmission and we did not specifically address maternal and fetal outcomes as a primary outcome measure. We did not systematically search for studies reporting this in our review and any conclusions around maternal and fetal outcomes should be interpreted with caution. The definition of vertical transmission varied across studies, with many not reporting the definition of vertical transmission used in the study. It should also be noted that all studies were conducted in the hospital setting, therefore this review does not provide evidence regarding transmission in the out-of-hospital setting. It is also well known that sample contamination is a hazard of performing PCR testing which is sufficiently sensitive to detect very low concentrations of nucleic acids; for example, to avoid contamination, a study of vertical transmission...

    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.

    Results from scite Reference Check: We found no unreliable references.

    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.

  2. Version published to 10.1101/2021.06.30.21259750 on medRxiv