FIGURE 1.
To assess VO+ and calcium absorption longitudinally across pregnancy and lactation, a stable calcium isotope (42Ca) was injected directly into compartment M1, which represents the mass of rapidly exchanging calcium pool. Clearance of the intravenous tracer in serum and urine over the 120-h interval postdosing was used to assess VO+. Compartments M2 and M3 are additional pools of calcium that represent time intermediaries in bone matrix formation. During pregnancy, VO+ reflects the loss of calcium into both maternal and fetal bone. During lactation, additional calcium loss from compartment M1 is added into the model to account for calcium loss into breast milk. The TEP reflects the pool sizes of compartments M1, M2, and M3. The fraction of the TEP that is used for bone calcium deposition is defined as VO+/TEP.