**2.6 Collection and preservation of samples**

Five milliliters of blood were drawn between 7:00 and 8:00 a.m. during the first trimester and placed in serum separator tubes before being placed on ice packs. Within an hour, serum samples were separated and stored in aliquots at −80°C for biochemical analysis. Each participant was given a clean, dry, wide mouth, leak-proof container to collect 5 mL of urine sample after the 20th week of pregnancy.
