The investigators propose a randomized clinical trial comparing the effect of 30 mcg ethinyl estradiol and LNG 150 combination oral contraceptive pills versus placebo, or LNG-IUS or Etonogestrel-releasing contraceptive implant (Implanon)on breast-milk intake and infant growth in exclusively breastfeeding mother-infant pairs. Mother-infant pairs will be randomly assigned either 30 microgram ethinyl estradiol combination oral contraceptive pills or identical placebo to start on post-partum day number 42 or Implanon implants or a LNG-IUS. All women will be offered nonhormonal contraceptives prior to randomization. The pairs will then be followed for four weeks. During this follow-up period, breast-milk intake will be quantified by administering deuterium oxide to exclusively breast-feeding mothers and measuring the enrichment of deuterium oxide in the saliva of their infants, otherwise known as the dose-to-mother method of Coward.17 Additionally, maternal and infant anthropometric measurements will be collected -- both as a value necessary to implement the breast-milk quantification method, as well as an outcome for analysis, and a daily diary will be kept by the women participating in the study that records infant feeds and diaper changes.