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1、 Iron requirements in pregnancy and strategies to meet them13Thomas H BothwellABSTRACTIron requirements are greater in pregnancyincreased requirements. As a result, iron supplementation duringthan in the nonpregnant state. Although iron requirements arereduced in the first trimester because of the a
2、bsence of menstru-ation, they rise steadily thereafter; the total requirement of a55-kg woman is 1000 mg. Translated into daily needs, therequirement is0.8 mg Fe in the first trimester, between 4 and5 mg in the second trimester, and 6 mg in the third trimester.Absorptive behavior changes accordingly
3、: a reduction in ironabsorption in the first trimester is followed by a progressive risein absorption throughout the remainder of pregnancy. Theamounts that can be absorbed from even an optimal diet, how-ever, are less than the iron requirements in later pregnancy and awoman must enter pregnancy wit
4、h iron stores of 300 mg if sheis to meet her requirements fully. This is more than most womenpossess, especially in developing countries. Results of controlledstudies indicate that the deficit can be met by supplementation,but inadequacies in health care delivery systems have limited theeffectivenes
5、s of larger-scale interventions. Attempts to improvecompliance include the use of a supplement of ferrous sulfate ina hydrocolloid matrix (gastric delivery system, or GDS) and theuse of intermittent supplementation. Another approach is inter-mittent, preventive supplementation aimed at improving the
6、 ironstatus of all women of childbearing age. Like all supplementa-tion strategies, however, this approach has the drawback ofdepending on delivery systems and good compliance. On a long-term basis, iron fortification offers the most cost-effective optionpregnancy is a common practice throughout the
7、 world.In the discussion that follows, 4 topics are addressed. The firstcovers the nature and extent of iron requirements during the3 trimesters of pregnancy. The second describes iron balance inpregnancy, including the adaptive changes that occur in ironabsorption during pregnancy. The third discus
8、ses assessing ironstatus during pregnancy, and the last reviews the various supple-mentation strategies that have been used to combat iron defi-ciency during pregnancy.IRON REQUIREMENTS DURING PREGNANCYIf the demand for iron were spread evenly throughout gesta-tion, iron requirements could be met mo
9、re easily by a sustainedrise in the rate of iron absorption. The need for iron, however,varies markedly during each trimester of pregnancy. Ironrequirements decrease during the first trimester because men-struation stops, which represents a median saving of 0.56 mgFe/d (160 mg/pregnancy) (1). The on
10、ly iron losses that must bemet during this period are the obligatory ones from the body viathe gut, skin, and urine, which amount to0.8 mg/d in a 55-kgwoman (14 gkg1d1 or 230 mg/pregnancy) (2). Early hemo-dynamic changes include generalized vasodilation, some increasein the plasma volume, and an inc
11、rease in red blood cell 2,3-diphosphoglycerate concentrations (3, 4). There is also some evi-dence that erythropoietic activity may be reduced during thisperiod, with a slight reduction in red blood cell mass (5), areduction in the number of reticulocytes (4), and a rise in theserum ferritin concent
12、ration (4, 6).for the future.Am J Clin Nutr 2000;72(suppl):257S64S.KEY WORDSIron, requirements, absorption, pregnancy,strategies, therapy, women, iron fortificationDuring the second trimester, iron requirements begin toincrease and continue to do so throughout the remainder of preg-nancy. The increa
13、se in oxygen consumption by both mother andfetus is associated with major hematologic changes. Most studiesin women supplemented with iron show a change in total bloodvolume of 45%, with an increase in plasma volume of 50%and an increase in red blood cell mass of35% (7). The rise inhemoglobin mass i
14、s similar at 30% (8). There has been someINTRODUCTIONThe overall iron requirement during pregnancy is significantlygreater than that in the nonpregnant state despite the temporaryrespite from iron losses incurred during menstruation. Ironrequirements increase notably during the second half of preg-nancy because of the expansion of the red blood cell mass andthe transfer of increasing amounts of iron to both the growingfetus and the placental structures. Iron is also lost in maternalbl
