Interpretation
Our findings are not in concordance with what has been reported in the early series of deliveries among COVID-19 infected women. Indeed, caesarean section rate ranges from 86% to 91% in the earlier series of cases(6,11). In a multicentre study(11) from China including 99 deliveries, the caesarean section rate was 86%, mostly for maternal pneumonia (39%), although only in 7% of them it was severe. In a systematic review(6) including 86 births mainly from China, but also from USA, Sweden and Corea, a caesarean section was performed in 91% of the deliveries, and fetal distress was found a main contributor to this exceedingly high rate. We found an overall caesarean section rate of 34%, which is in keeping with the one reported in two more recent retrospective multicentre studies, one in New-York involving 18 deliveries(18) and the other in Northern Italy with 42(19) (caesarean section rate of 42% and 43%, respectively). Also in agreement with our results, both studies found overall good maternal and neonatal outcomes. In fact, the caesarean rate observed in our cohort after excluding those women who were delivered preterm because of worsening of maternal respiratory status, was similar (4/18, 22.2%) to our baseline caesarean rate expected as a tertiary center (25.8%). Therefore, our findings support current recommendations on that the mode of delivery in respiratory stable women should be taken depending on obstetric conditions.
It could also be argued that concerns on the risk of vertical transmission during vaginal delivery may have contributed to these initially reported increased rates of caesarean section. However, in previous epidemics of other coronavirus diseases, SARS and MERS, vertical transmission was not confirmed although the evidence against relies on a limited number of small series(20). It is well known that vaginal route increases the risk of transmission through cervical and vaginal contaminated secretions, as in the case of herpes simplex or HIV viruses. However, SARS-CoV-2 is a respiratory virus that mainly replicates in the respiratory tract and it has not been detected in genital secretions(21) . Another potential way of intrapartum transmission could be through contaminated stool since SARS-CoV-19 RNA has been isolated from feces, but those are probably not infectious forms of the virus(22). Bloodstream transplacental transmission during uterine life or through placental disruption at the time of delivery is also very unlikely, given that viremia is uncommon. A single positive RNA-PCR reported case in amniotic fluid in a 32 weeks preterm newborn delivered by caesarean section at the time of very severe maternal infection could correspond to a true vertical transmission secondary to a high maternal viremia or inflammatory placental abnormality in this critically ill mother. However, since amniotic fluid was collected for testing during the caesarean section, maternal contamination could not be excluded(10). Early-onset symptoms in the newborn, and negative PCR at birth, but positive some days after, also suggests a true vertical transmission, although horizontal or iatrogenic transmission could not be discarded. Moreover, 2 articles reporting 3 neonates from mothers with COVID-19 and positive IgM antibodies(23)(24) is also of concern, given that IgM antibodies do not cross the placenta and are of fetal origin. However, IgM antibodies assays have false positives, and the tests performed in these studies lacked standardization(25).
In our study, in which newborns were swabbed in the first 48 hours of life, we did not observe any positive RT-PCR in nasopharyngeal samples irrespectively of the way of delivery. Likewise, Yan et al. in the largest series reported so far described negative results of neonatal SARS-CoV-2 PCR in all 86 tested cases(11). In the ten samples of amniotic fluid and cord blood tested, they could not demonstrate the presence of SARS-CoV-2. As far as we know there are no reported positive newborns after vaginal deliveries. These findings suggest that vaginal delivery is associated with a low risk of intrapartum SARS‐Cov‐2 transmission to the newborn.