Blood collection
Maternal and VC blood samples were collected at delivery by trained phlebotomists. Trace metal-free EDTA-coated tubes were used to draw maternal samples, and whole-blood aliquots were drawn prior to centrifugation. Cord blood was collected within 30 min of delivery from a site on the umbilical cord attached to the placenta after wiping maternal blood away with dry gauze. The umbilical vein was cannulated to collect blood into a lavender top EDTA tube. Whole blood was stored at −70°C or colder.