RESULTS
We included 28 of 36 (77.8%) women, who had SARS-CoV-2 positive pharyngeal swabs during pregnancy in the study period. Three participants were not tested by RT-PCR. Participant 6 was tested by a nasopharyngeal antigen-test, and participants 16 and 18 were tested at a private test centre. Participants and non-participants did not differ regarding baseline characteristics (table 1). Twenty-two participants (78.6%) were included at delivery (table 2), while six participants were included and examined during pregnancy with examinations repeated at delivery (table 3). Participants tested positive for SARS-CoV-2 by a pharyngeal swab between gestational age (GA) 25 weeks (w) and 0 days (d) to 41w4d, and the onset of symptoms was reported from 16 days before and until three days after the positive swab.
Vaginal swabs were obtained from all participants, and SARS-CoV-2 was detected in 2 of 28 cases – at one and eight days, respectively, after the positive pharyngeal swab (7.1%). One vaginal swab test was inconclusive. No positive vaginal swabs were found during vaginal delivery, independently of the timing with onset of symptoms or a positive pharyngeal swab (table 2 and 3).
Maternal antibodies were analysed in 28 women (table 2 and 3). Within 8 days of a positive pharyngeal swab, SARS-CoV-2 antibodies were detected in only 1 (participant 6, table 2) of 13 women (7.7%). Whereas, antibodies were observed in 19 of 21 (90.5%) women who had a positive pharyngeal swab more than 8 days prior to the antibody test (table 2 and 3). Two women had no antibody response in blood samples at day 57 and 74 days after infection, respectively (participants 25 and 26).
Antibodies were analysed in 25 umbilical cord blood samples. Antibodies were not detected in umbilical cord blood from pregnancies where the woman delivered within 16 days of a SARS-CoV-2 positive pharyngeal swab (n=7). However, antibodies were present in 16 of 17 (94.1%) cord blood samples of pregnancies where the woman was seropositive and delivered more than 16 days after infection (table 2 and 3). The test results (S/C) of antibodies in maternal and cord blood at delivery were highly correlated (figure S3, R2=0.64, p<0.00005). There was a positive correlation between the test results (S/C) for antibodies in cord blood and the number of days from SARS-CoV-2 positive pharyngeal swab to delivery (figure S4, R2=0.43, p=0.002), whereas the correlation between the test result (S/C) for antibodies in maternal blood and the number of days between diagnosis and delivery was not statistically significant (figure S4, R2=0.20, p=0.054). Three cord blood samples from children of nineteen seropositive mothers were without detectable antibodies (15.8%, participants 6, 8 and 10).