Defining a Dosing Regimen With Maximal Absorption for Oral Iron Supplementation During Pregnancy

3 doses of 60mg iron as ferrous fumarate are given on one consecutive day and one alternate day (e.g., days 1, 2, 4); 3 doses of 120mg iron as ferrous fumarate are given on one consecutive and one alternate day (e.g., days 20, 21, 23); 3 doses of 120mg iron as ferrous fumarate are given on one consecutive and one 3rd day (e.g., days 37, 38, 41). Iron doses are labeled with 4mg of a stable isotope in 200ml deionized water (57Fe, 58Fe or 54Fe). Participants will be randomly assigned to start with 60mg iron daily vs alternate day dosing, 120mg daily vs alternate day dosing or 120mg daily vs every-third day dosing.