1. Unit of Research in Medical Nutrition; Centro Médico Nacional Siglo XXI; Mexican Institute of Social Security; Mexico City Mexico
2. Hospital of Obstetrics and Gynaecology #3; Centro Médico La Raza; Mexican Institute of Social Security; Mexico City Mexico
3. Hospital of Obstetrics and Gynaecology #4; Luis Castelazo Ayala; Mexican Institute of Social Security; Mexico City Mexico