SARS-CoV-2 and pregnancy: Can the novel coronavirus cross the placental barrier?

By Rachel West

Submitted by Rachel West, April 2020

As the novel coronavirus, SARS-CoV-2, continues to spread and the hope for a potential cure or vaccine still months away, pregnant women are justifiably concerned about their safety and the risk of transmitting the virus to their fetus. News reports about vertical transmission of the virus have been conflicting at best and fearmongering at worst. Unfortunately, there is still much we don’t know about how SARS-CoV-2 and the associated disease COVID-19 might affect pregnancy. As the novel coronavirus persists, research is being conducted and published at a fevered pace and some of the data are encouraging.

Pregnant women are not at increased risk of adverse outcomes after contracting SARS-CoV-2.            

Previous coronaviruses, including SARS-CoV and MERS-CoV, caused increased risk of severe disease during pregnancy, leading to elevated rates of first trimester miscarriage and intrauterine growth restriction1. However, in a February World Health Organization (WHO) report, the WHO stated that pregnant women do not appear to be at higher risk for severe disease after contracting SARS-CoV-22, with only a small percentage of pregnant women positive for the virus meeting the criteria for severe disease.

No traces of SARS-CoV-2 virus have been found in sources of transmission from mother to baby.                                 

A study published in The Lancet reported no evidence of virus in the amniotic fluid, cord blood, neonatal throat swab, or breastmilk samples taken from six pregnant COVID-19 patients, suggesting no vertical transmission of SARS-CoV-2 from mother to baby3. In support of this evidence, a bioRxiv preprint reported a rhesus macaque model of COVID-19 indicating no detectable viral load in the blood of infected macaques. These data suggest that the virus is not circulating throughout the maternal blood supply and therefore would not be capable of vertical transmission4.

However, some infants born to infected mothers do have antibodies against SARS-CoV-2.                                  

One conundrum making it difficult to completely rule out the possibility of vertical transmission is the presence of elevated antibodies in infants born to infected mothers. Two studies, both published in JAMA, reported virus-specific antibodies in infants born to mothers positive for SARS-CoV-25,6.  Interestingly, while the serology reports that these infants had elevated levels of antibodies, all RT-PCR results from nasopharyngeal swabs were negative, indicating that these infants were not actively infected with the virus. Whether the reports of elevated antibodies are evidence that SARS-CoV-2 can cross the placental barrier or are just a consequence of transmission of antibodies from infected mothers has yet to be determined.

What are the next steps to determine if SARS-CoV-2 can cross the placental barrier?                                       

Several hospitals across the country have begun programs to track SARS-CoV-2 positive women at all stages of pregnancy through term, deliveries, and the early stages of their infants’ lives. The results from these tracking programs will provide critical insight into the effects of SARS-CoV-2 infection at all stages of pregnancy. The debate of whether SARS-CoV-2 is capable of vertical transmission will probably remain murky until the findings from these tracking programs begin to circulate. Until then, we can find solace in the fact that SAR-CoV-2 infections in infants appear to both be rare and mild.

1Schwartz D, Graham A. Potential maternal and infant outcomes from coronavirus 2019-nCOV (SARS-CoV-2) infecting pregnant women: lessons from SARS, MERS, and other human coronavirus infections. Viruses. 2020 Feb 28, 12:194.

2Report of the WHO-China Joint Mission on Coronavirus Disease 2019 (COVID-19).

3Chen J, Guo J, Wang C, et al. Clinical characteristics and intrauterine vertical transmission potential of COVID-19 infection in nine pregnant women: a retrospective review of medical records. The Lancet. 2020 Mar 7, 395: 809-815.

4Munster V, Feldmann F, Williamson B, et al. Respiratory disease and virus shedding in rhesus macaques inoculated with SARS-CoV-2. bioRxiv. 2020 Mar 21, doi: 

5Zeng H, Xu C, Fan J, et al. Antibodies in infants born to mothers with COVID-19 pneumonia. JAMA. 2020 Mar 26, doi:10.1001/jama.2020.4861.

6Dong L, Tian J, He S, et al. Possible vertical transmission of SARS-CoV-2 from an infected mother to her newborn. JAMA. 2020 Mar 26, doi:10.1001/jama.2020.4621.

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