Cohort 2: Serological assessment in asymptomatic pregnant women
Samples were available for serological analysis in 598 women in the
asymptomatic cohort. Anti-SARS-CoV-2 IgG antibodies were detected in 12
women using the Roche platform and ten women using the Alinity and
Architect platform (Table S2). The seroprevalence rate using two
independent assays was 1.67% (10/598 95% CI 0·8-3·1%).
Anti-SARS-CoV-2 IgM antibodies were observed in twenty-one asymptomatic
women (21/598 3.51% CI 2.3-5.5%) (Supplementary table S3a). Of these
21 women, 8 were also IgG positive (8/21, 38%) using both the Roche,
Architect and Alinity platforms. Th majority of women who were antibody
positive were > 24 weeks gestation. Demographics of all
women are presented in supplementary table S4
Nine women from the asymptomatic cohort returned for follow up antibody
testing between 101-122 days after the baseline test (Table 1). Four
(4/9, 44%) remained IgM positive (Figure 2a). One woman was IgM
positive only at baseline testing. Her follow up IgM antibodies were
negative. In view of this, and the initial negative PCR and IgG anti
SARS-CoV-2, it is likely that this also represents a false positive IgM
result. The majority (6/7, 85.7%) of the seven women who were IgG
positive at baseline no longer exhibited anti SARS-CoV-2 IgG antibodies
(Figure 2b). Retrospective histories taken at follow-up suggests many of
these women may have been mildly symptomatic at the time of the initial
study