until weeks or months after birth (Begum et al., 1968; Ford et al., 1973; Moncrieff and Fadahunsi, 1974; Sann et al., 1976; Pereira and Zucker, 1986; Park et al., 1987; Campbell and Fleischman, 1988; Specker, 1994; Teotia et al., 1995; Beck-Nielsen et al., 2009). Thus, neonatal rickets is of limited utility in the development of DRIs for pregnancy.
Maternal and cord blood 25OHD levels Regarding pregnancy outcomes, maternal and cord blood 25OHD levels may be of interest. AHRQ-Ottawa reported inconsistent evidence on changes in serum 25OHD levels during pregnancy, with two studies reporting no change and one study reporting a decline. In a few other studies, maternal serum 25OHD levels have responded to supplemental vitamin D (Marya et al., 1981, 1988; Mallet et al., 1986; Yu et al., 2009). In observational studies, babies born of vitamin D–deficient mothers have the lowest serum 25OHD levels and are at higher risk for complications sooner after birth than are babies born of vitamin D–replete mothers. Maternal serum 25OHD levels were stable and largely unaffected by pregnancy (Hillman et al., 1978; Brooke et al., 1980; Ardawi et al., 1997; Morley et al., 2006), even when the baseline serum 25OHD level was very low (20.1 ± 1.9 nmol/L) (Brooke et al., 1980).
Overall, fetal BMC and related skeletal outcomes are informative for DRI development for pregnancy.
POTENTIAL INDICATORS FOR LACTATION: CALCIUM The key physiological changes to meet the calcium demands of lactation occur through increased bone resorption, and most of the calcium in human milk comes from the maternal skeleton (Kalkwarf, 1999; Prentice, 2003; Kovacs, 2005; Kovacs and Kronenberg, 2008). Thus, lactation is a period of transient bone mineral loss and not, per se, a period of bone maintenance, although BMD is restored post-weaning (Kalkwarf, 1999). However, lactation is included in the category of bone maintenance in order to discuss pregnancy and lactation contiguously, and because bone mineral is restored in the immediate period post-lactation. Potential indicators related to calcium requirements during lactation are outlined below.
Maternal BMD The need to provide calcium to the infant—a need that is two to three times greater than the daily amount needed for fetal development during pregnancy—is met by the maternal adaptation of increased bone resorption (Specker et al., 1994; Kalkwarf et al., 1997), resulting in a 5 to 10 percent decline in BMD during the first 6 months of exclusive breastfeeding