The crucial role of folate in the biosynthesis of precursors for DNA suggests that folate requirements may vary with age, though folate use is most obviously increased during pregnancy and lactation. Maintaining adequate folate status in women in their child-bearing years is particularly important since a large proportion of pregnancies are unplanned and many women are likely to be unaware of their pregnancy during the first crucial weeks of fetal development. Pregnancy requires an increase in folate supply that is large enough to fulfil considerable mitotic requirements related to fetal growth, uterine expansion, placental maturation, and expanded blood volume. The highest prevalence of poor folate status in pregnant women occurs among the lowest socioeconomic groups and is often exacerbated by the higher parity rate of these women. Indeed, the megaloblastic anemia commonly found amongst the malnourished poor during pregnancy probably reflects the depletion of maternal stores to the advantage of the fetal-placental unit, as indicated by the several-fold higher serum folate levels in the newborn compared with the mother. Considerable evidence indicates that maternal folate deficiency leads to fetal growth retardation and low birth weight. The higher incidence of low-birth-weight infants among teenage mothers compared with their adult counterparts is probably related to the additional burden that adolescent growth places on folate resources.

The lack of hard evidence about the extent of supplementation required in pregnancy prompted the development of a laboratory-based assessment of metabolic turnover, which involved the assay of total daily folate catabolites (along with intact folate) in the urine of pregnant women. The rationale of the procedure was that this catabolic product represents an ineluctable daily loss of folate, the replacement of which should constitute the daily requirement. Correcting for individual variation in catabolite excretion and the bioavailability of dietary folate, the recommended allowances based on this mode of assessment are in close agreement with the latest recommendations of the USA/Canada and FAO/WHO. The data produced by the catabolite-excretion method may provide a useful adjunct to current methods based on intakes, clinical examination, and blood folate measurements to provide a more accurate assessment of requirement.

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