Maternal COVID-19 serological Changes. Comparison between seroconversion Rate in First and Third Trimester of Pregnancy and Subsequent Obstetric Complications: A Cohort Study

Pregnant women are especially vulnerable to respiratory diseases. We aimed to study seroconversion rate during pregnancy in a cohort of consecutive pregnancies tested in the first and third trimesters and to compare maternal and obstetric complications between women who seroconverted in the first versus the third trimester. This is an observational, cohort study carried out at Hospital Universitario de Torrejón, in Madrid, Spain, during the first peak of the COVID-19 pandemic. All consecutive singleton pregnancies with a viable fetus attending their 11-13 weeks scan between January 1st and May 15th, 2020, were included and monthly follow up until delivery. Antibodies against SARS-CoV-2 (IgA and IgG) were analyzed on stored serum samples obtained from the first and third trimester routine antenatal bloods in 470 pregnant women. Antibodies against SARS-CoV-2 were detected in 31 (6.6%) women in the first trimester and in 66 (14.0%) in the third trimester, including 48 (10.2%) that were negative in the first trimester (seroconversion during pregnancy). Although the rate of infection was significantly higher in the third versus the first trimester (p = 0.003), no significant differences in maternal or obstetric complications were observed in women testing positive in the first versus the third trimester.