In this study, we found that before antiviral treatment (at 26–28 weeks of gestation), compared to the Treg amounts in NAF mothers, those in AF mothers decreased, and T cells in AF mothers secreted significantly higher amounts of pro-inflammatory cytokines (IFN-γ, IL-21, IL-2) and less amounts of anti-inflammatory cytokines (IL-10). The gene discussed is IL21; the disease is atrial fibrillation.