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.