Iron for the Maternal Red Cell Mass and Anemia

The red cell mass in pregnancy is not a static number and can be affected by the amount of iron supplementation that has occurred during the pregnancy [4]. For example,

Table 16.1

Estimated Median Iron Requirements (mg) During Pregnancy

Table 16.1

Estimated Median Iron Requirements (mg) During Pregnancy

1st trimester

2nd trimester

3rd trimester

Total

Fetus

25 mg

75 mg

145 mg

245 mg

Placenta and umbilicus

5 mg

25 mg

45 mg

75 mg

Red cell mass

5-10 mg

225 mg

225 mg

450 mg

Total

35-40 mg

325 mg

415 mg

Week of gestation

Fig. 16.1. Hemoglobin concentration in healthy women in developed countries. The solid curve is the median Hb concentration, while the dashed line is the 5th percentile

Week of gestation

Fig. 16.1. Hemoglobin concentration in healthy women in developed countries. The solid curve is the median Hb concentration, while the dashed line is the 5th percentile when supplemental iron was provided to a group of women, the expansion of the red cell mass was approximately 570 mg of Fe, whereas when no supplementation was provided, the expansion was only 260 mg of Fe. It has been suggested that for every 10 g/l increase in maternal Hb desired, there is a need for an additional 175 mg of absorbed iron [5]. The amount of additional iron needed for expansion of the red cell mass is also dependent on the numbers of fetuses in the womb. If twins are expected, then the expansion is estimated to be 680 ml, while triplets increase the blood volume to around 900 ml. The World Health Organization recommends iron supplements of between 3060 mg/day if the woman has iron stores (e.g., ferritin >30 mcg/l). The recommendation is quite close to the Institute of Medicine recommendation of 30 mg/day for the second and third trimesters if stores are also present at the first clinic visit. If stores are absent, then a much more aggressive approach is usually taken with intakes of 120-240 mg/day advocated. It is easy to assume that more iron and higher Hb is better, but there are data that actually demonstrate a negative outcome to an overly elevated Hb concentration [6]. Consumption of large doses of iron supplements have been related to oxidative damage, and the gastrointestinal side effects may be related to the poor compliance in many populations of pregnant women [7, 8]. The alternative approach of non-daily low-dose iron supplementation appears to be effective in situations of only modest iron deficits.

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