Objective: To determine SARS-CoV-2 seroprevalence in a UK pregnancy cohort and assess associations with demographic factors and vaccination timing. Design: Observational cohort study. Setting: UK inner-city maternity centre. Sample: 960 pregnant women attending nuchal scans from July 2020-January 2022. Methods: Blood samples were tested for IgG antibodies against SARS-CoV-2 nucleocapsid (N) and spike (S) proteins. Self-reported demographics, vaccination status and previous Covid-19 infection were extracted from health records. Multivariable regression models determined factors associated with seroprevalence and antibody titers. Main outcome measures: IgG N- and S-protein antibody titers. Results: 196/960 (20.4%) women were SARS-CoV-2 seropositive from previous infection. Of these, 70 (35.7%) self-reported previous infection. Amongst unvaccinated women, black women were most likely to be SARS-CoV-2 seropositive (aRR 1.88 [95% CI, 1.35-2.61], P < 0.001). Women from black and mixed ethnic backgrounds were least likely to have a history of vaccination with seropositivity to S-protein (aRR 0.58 [95% CI, 0.40-0.84], P = 0.004 and aRR 0.56 [95% CI, 0.34-0.92], P = 0.021 respectively). Double vaccinated, previously infected women had higher IgG S-protein antibody titers than unvaccinated, previously infected women (mean difference: 4.76, 95% CI = [2.65, 6.86], P < 0.001). Vaccination timing before vs during pregnancy did not significantly affect IgG S antibody titers (F(1, 77) = [0.07], P = 0.785). Conclusions: This inner-city pregnancy cohort demonstrates high rates of asymptomatic SARS-CoV-2 infection with women of black ethnicity having higher infection risk and lower vaccine uptake. SARS-CoV-2 antibody titers were highest among double vaccinated, previously infected women.
