Increasing numbers of pregnant women with COVID-19 are being reported around from the world. The majority of neonates delivered to pregnant women infected with the new coronavirus SARS-CoV-2 have been negative for the virus, but a small number have tested positive for infection. It is important to determine whether vertical transmission of COVID-19 occurs and the mechanisms for its development. Based on a number of clinical and laboratory findings it has been suggested that transplacental transmission may be occurring, but a method to confirm this is necessary. This communication analyzes and evaluates the covariables that have been discussed as potential indicators of vertical and, specifically, intrauterine transmission including the timing of onset of neonatal illness, neonatal viral test positivity, neonatal antibody testing for IgG and IgM, and viral analysis of swabs of whole specimens of placental tissue. None of these methods can provide confirmatory evidence that infection developed prior to labor and delivery, or that transplacental transmission occurred. This commentary proposes that diagnosis of early-onset neonatal COVID-19 infection should be limited to neonates with positive RT-PCR testing for SARS-CoV-2 within the initial 72 hours of life. It also proposes that the occurrence of intrauterine transplacental SARS-CoV-2 among infected mother-infant dyads be based upon identification of SARS-CoV-2 in chorionic villous cells using immunohistochemistry or such nucleic acid methods such as in situ hybridization. Evaluating placentas from neonates with COVID-19 using these methods will be instrumental in determining the potential role and prevalence of transplacental transmission of the coronavirus.

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Author notes

The authors have no relevant financial interest in the products or companies described in this article.