The primary aim of this study is to obtain measures of amino-terminal telopeptides of procollagen 1 (P1NP), a marker of bone formation, in lactating and non-lactating post-partum African-American women both at 6-8 and at 12-14 weeks post-partum, and to compare these values to those of normal controls. The secondary aim is to obtain at the same time points, measurements of Parathyroid Hormone-related Protein (PTHrP), additional markers of bone turnover [e.g. N-telopeptide of collagen cross-links (NTx), C-telopeptide of collagen cross-links (Ctx),bone specific alkaline phosphatase (BSAP) and osteocalcin (OC)], calcium and vitamin D metabolism in these subjects. These results will be compared with a non-African-American cohort of post-partum women and normal controls.