Clinical interpretation
Data regarding vertical transmission of SARS-CoV-2 is scarce. Most data are based on case reports and small case series. A recent review analyzed 38 studies that assessed COVID-19 and pregnancy. The rate of vertical transmission of SARS-CoV-2 differed by sample source and test type; rates were 2.9%, 7.7%, 2.9%, and 3.7% for neonatal nasopharyngeal swab testing (N=936), placental sampling (N=26), cord blood IgM serology (N=34) and neonatal IgM serology (N=82), respectively. Amniotic fluid (N=51) and neonatal urine (N=17) analyses showed no evidence of vertical transmission18. The highest vertical transmission rates (9.7% of N=31) were observed when testing neonatal fecal/rectal samples19,20. In our study the rate of vertical transmission measured by neonatal nasopharyngeal swab testing only, was 3%, while serology analysis added at least an additional 10% of vertical transmission. These findings are similar to those reported in the literature and emphasize the importance of analyzing serology for the assessment of fetal infection. It is particularly important in mothers who had COVID-19 disease whose baby showed a negative neonatal nasopharyngeal swab test. Since positive neonatal serology may suggest fetal infection, these neonates should undergo close surveillance for possible long-term implications.
SARS-CoV-2 binds to host cells through the angiotensin-converting enzyme-2 (ACE-2) receptor, after which, serine proteases TMPRSS2 contribute to priming the spike protein, to enable it to fuse with the host cell membrane and replicate1, 21. Vertical transmission is possible as the ACE-2 receptor is expressed on various cells, such as cells of the ovary, uterus, vagina, placenta22 and venous and arterial endothelium, as well as of the smooth muscle of the umbilical cord14.