tion decreases with the progression of pregnancy due to hemodilution as well as active transfer to the fetus. Therefore, in order to transfer adequate vitamin C to the fetus, additional vitamin C is needed during pregnancy. In the absence of data on near maximal neutrophil saturation during pregnancy, the method of determining the EAR for pregnancy is based on adding the EAR for near-maximal neutrophil concentration of the nonpregnant woman to the amount of vitamin C necessary to transfer adequate vitamin C to the fetus. In the absence of precise data regarding transfer of maternal vitamin C to the fetus, and with the knowledge that intakes of 7 mg/day of vitamin C will prevent young infants from developing scurvy (Goldsmith, 1961; Rajalakshmi et al., 1965; van Eekelen, 1953), the EAR for pregnancy was estimated to increase 10 mg/day over the vitamin C requirement for the nonpregnant woman.

The RDA for vitamin C is set by assuming a coefficient of variation (CV) of 10 percent (see Chapter 1) because information is not available on the standard deviation of the requirement for vitamin C; the RDA is defined as equal to the EAR plus twice the CV to cover the needs of 97 to 98 percent of the individuals in the group (therefore, for vitamin C the RDA is 120 percent of the EAR). The calculated values for the pregnancy RDA have been rounded up to the nearest 5 mg.

Certain subpopulations of pregnant women may have increased requirements for vitamin C. This group includes users of street drugs and cigarettes, heavy users of alcohol, and regular users of aspirin (Flodin, 1988). Women who smoke more than 20 cigarettes per day may require twice as much vitamin C as nonsmokers to maintain a replete body pool of vitamin C (Kallner et al., 1981). It has been reported that plasma vitamin C in pregnant smokers ex-