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Background: Passively acquired maternal antibodies through the placenta and/or breastfeeding may protect neonates against SARS-CoV-2 before they are considered eligible for active immunization.

Objectives: This study aimed to determine the concentration and correlation of maternal and cord blood anti-SARS-CoV-2 IgG antibodies in Iranian seropositive women. In this preliminary study, attempts were also made to assess the effects of some variables on the transplacental transfer efficiency.

Methods: From September 2021 to November 2021, pregnant women presenting to Kamali Hospital in Karaj, Iran, were enrolled in this monocentric study. The maternal and neonatal demographic characteristics were collected. The maternal and cord blood spike protein-specific antibody levels, measured at delivery (119 paired samples), were evaluated by the enzyme-linked immunosorbent assay (ELISA).

Results: Based on the transplacental antibody transfer ratios, the participants were divided into 2 groups: Transfer ratio similar to 1 (n = 53) and transfer ratio > 1 (n = 66). The results revealed that anti-SARS-CoV-2 IgG antibodies were transferred across the placenta in all seropositive pregnant Iranian women, and a significant correlation was found between maternal and cord blood-specific IgG antibody levels (r = 0.9646; P < 0.05). A relatively efficient transplacental transfer ratio was observed in Iranian seropositive women (transfer ratio > 1 in 66 out of 119 individuals; 55.46%). Although there were significant differences in the transplacental transfer ratio regarding the neonatal birth weight and maternal body mass index (BMI), more extensive investigations with a larger sample size are needed to confirm the significant association of these variables with the transplacental transfer efficiency of specific SARS-CoV-2 IgG antibodies.

Conclusions: The present study highlighted the importance of vaccination during pregnancy to improve neonatal immune responses against SARS-CoV-2.