and Recker, 1982; Stanbury, 1971; Wilkinson, 1976). Daily fetal phosphorus requirements of about 62 mg (2 mmol) are needed to produce a term infant at birth with a phosphorus content of 17.1 g (552 mmol) (Fomon et al., 1982). The EAR for phosphorus in adults ages 19 through 30 years is approximately 580 mg (18.7 mmol)/day at an absorption of 60 percent (resulting in an absorbed phosphorus of 353 mg [11.4 mmol/day]). Assuming a 70 percent absorption of phosphorus during pregnancy (Heaney and Skillman, 1971), a similar EAR of 580 mg (18.7 mmol)/day would lead to an absorbed phosphorus of 412 mg (13.3 mmol)/day. This increase in absorbed phosphorus during pregnancy (59 mg [1.9 mmol/day]) approximately equals the estimated fetal phosphorus requirement of 62 mg (2 mmol)/day.

Serum phosphorus concentrations during pregnancy are within the normal range at mean daily intakes of approximately 1,550 mg (50 mmol) (95 percent CI range of 1,260 to 1,840 mg [40.6 to 59.4 mmol]) (Cross et al., 1995a). No studies have specifically investigated the effect of dietary intake of phosphorus on phosphorus balance during pregnancy.

No evidence at this time supports an increase of the EAR and RDA during pregnancy above the level recommended during the nonpregnant state. Intestinal absorption of phosphorus increases by about 10 percent during pregnancy (Heaney and Skillman, 1971). That change should be sufficient to provide the necessary phosphorus for fetal growth.

Utilizing the 1994 CSFII intake data for 33 pregnant women, adjusted for day-to-day variations (Nusser et al., 1996), the value derived for the EAR of 580 mg (18.7 mmol)/day for pregnant women ages 19 through 50 years represents a low dietary intake of phos-