Immunoglobulin G IgG1 and IgG3 subclasses to the antigens were measured in maternal peripheral and cord plasma samples as previously described [29 (link)]. In brief, after incubating beads with 50 µL of a 1:100 dilution of plasma, beads were washed and incubated with 100 µL mouse anti-human IgG1 (Molecular Probes) at 1:250 dilution or mouse anti-human IgG3 (clone HP6050 I7260; Sigma) at 1:2000 dilution in PBS-1% BSA for 1 hour at 25°C. After washing, beads were resuspended in 100 µL phycoerythrin-labeled donkey anti-mouse IgG H + L (catalog number 715-116-150, Jackson ImmunoResearch Laboratories) at a 1:250 dilution in PBS-1% BSA for 1 hour, washed, and resuspended in 100 µL PBS-1% BSA. Median fluorescence intensity were determined as described above.