1. Central Epidemiology Laboratory, Mexican Social Security Institute, Mexico City 02990, Mexico
2. Reproductive and Perinatal Health Research Department, National Institute of Perinatology, Mexico City 11000, Mexico
3. Quality of Supplies and Specialized Laboratories Coordination, Mexican Social Security Institute, Mexico City 07760, Mexico
4. Southern Medical Line, Mexico City 11000, Mexico
5. Immunobiochemistry Department, National Institute of Perinatology, Mexico City 11000, Mexico
6. Specialized Laboratories Division, Mexican Social Security Institute, Mexico City 07760, Mexico