Collect specimen in a red top tube from a patient with a maternal gestation of between 16 weeks 0 days and 22 weeks 6 days. Centrifuge, aliquot serum into a plastic vial within 2 hours of collection and refrigerate. Please provide a completed QUAD/AFP Requisition available online at https://mlabs.umich.edu/media/170 or the following information: gestational age (weeks and days on first ultrasound date >6 weeks 0 days; if ultrasound information is not available record first days of last menstrual period), maternal weight, maternal date of birth, insulin-dependent diabetes status prior to pregnancy, multiple gestation (single, twin, triplets), race, and previous history of Down syndrome or neural tube defect (NTD) pregnancy for the patient.