key: cord-349656-baoqgu8v
authors: Wang, Chen; Zhou, Yi‐Hua; Yang, Hui‐Xia; Poon, Liona C.
title: Intrauterine vertical transmission of SARS‐CoV‐2: what we know so far
date: 2020-04-07
journal: Ultrasound Obstet Gynecol
DOI: 10.1002/uog.22045
sha: 
doc_id: 349656
cord_uid: baoqgu8v

nan

study also demonstrated that vaginal secretion samples also tested negative for SARS-CoV-2 RNA. [2] In a study by Chen et al., [3] paired neonatal pharyngeal swab samples and placental tissues of three pregnant women with COVID-19 were used as samples to evaluate the potential risk of intrauterine vertical transmission, and all samples tested negative for SARS-CoV-2 RNA. Notably, a neonate born to a pregnant woman with COVID-19 tested positive for SARS-CoV-2 RNA in the pharyngeal swab sample at 36 hours after birth was subsequently confirmed that the qRT-PCR testing of the placenta and cord blood was negative for SARS-CoV-2, suggesting that intrauterine vertical transmission might not have occurred. [4, 5] Thus, based on these existing data, there is currently no evidence for intrauterine infection caused by vertical transmission in women with COVID-19.

However, some questions remain unanswered. Most of the cases in the studies as described above had mild to moderate symptoms, and all manifested during the third trimester of pregnancy, and therefore the time interval from clinical manifestation of COVID-19 infection to delivery was short. Since the placental barrier may temporarily delay the transfer of the virus from the mother to the fetus, as observed in cytomegalovirus infection, it is uncertain whether there could be a risk of vertical transmission when the COVID-19 infection occurs in the first or second trimester, or when there is a long clinical manifestation-to-delivery interval.

Additionally, there appear some ways through which SARS-CoV-2 can potentially cause intrauterine infection by transplacental vertical transmission. A study by Zhao et al. has in the study by Dong et al., the observed decline of SARS-CoV-2 IgG from 140.32 AU/mL (normal range 0-10 AU/ml) at 2 hours of life to 69.94 AU/mL on day 14 of life and of IgM from 45.83 AU/mL (normal range 0-10 AU/ml) at 2 hours of life to 11.75 AU/mL on day 14 of life is not consistent with the typical profile of the body's antibody response to acute viral infection. [9] As the half-life of IgG antibodies is around 21-23 days, and the time lag between the development of SARS-CoV-2 IgG and IgM antibodies is about one week, [11] [12] the rapid decline ([140.32-69.94]/140.32=50%) of SARS-CoV-2 IgG in the infant within 14 days, while there had been a decline in IgM antibodies, strongly indicates that the neonatal SARS-CoV-2 IgG was transplacentally derived from the mother, and was not actively induced by the presumed neonatal infection. In our opinion, these two studies have not provided concrete evidence to prove that SARS-CoV-2 infection can be acquired in utero.

Furthermore, in a cohort study by Zeng et al., [13] 3 of 33 (9%) infants were diagnosed with neonatal early-onset infection with SARS-CoV-2 based on positive qRT-PCR results of the nasopharyngeal and anal swabs in two consecutive tests at day 2 and 4 of age. Though, strict infection control and prevention measures were implemented during the delivery, one cannot completely exclude postpartum infections because of the delay in testing. All three infants tested negative for SARS-CoV-2 RNA by day 6/7. [13] Whether the neonatal infection can cause the same virologic profiles as adult infection requires further investigation.

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