Title: Iron in Pregnancy

Key words: Anaemia, iron supplementation, iron metabolism, Vitamin C, iron stores, haemoglobin

Date: June 1999

Category: 10. Reproduction

Type: Article

Author: Dr van Rhijn

 

 

Iron in Pregnancy

The Need for Supplementation

Introduction

The need for routine iron supplements remains a longstanding controversy1, partly due to disagreements regarding the definition of anaemia2, markers of iron deficiency and aspects of iron metabolism3, despite evidence for an increased iron requirement during pregnancy4.

Normal Physiology

Increase in plasma volume (1250 ml) and red cell mass (240 ml – 400 ml iron dependant) during pregnancy, result in a ‘physiological anaemia’ due to haemodilution5. The extra iron needed to meet this demand amounts to 1040 mg, much of it (43%) to increase the mother’s haemoglobin mass during the last trimester. The absorption of iron is unequally distributed. During the first trimester it decreases by 7.6 %, then in the second it increases to 21.1 % and during the last trimester it goes up to 37.4 %, matching the growth of the foetus6. These values may be optimistic as iron absorption was enhanced with vitamin C in this study.

Despite this physiological adaptation, the deficit remains approximately 400 – 500 mg of iron which, in most industrialised countries, cannot be obtained by diet alone7. One in three British women in a survey had levels below the LRNI8. Soluble serum transferrin receptor9 and serum ferritin10 are indicators of storage iron, where a cut-off point of 25 - 30 microg/l indicates low iron stores11.

The development of iron deficiency anaemia during pregnancy (30% prevalence in 3rd trimester12) is dependent upon whether the mother enters pregnancy with adequate iron stores13. Infants born to mothers with iron depleted stores have reduced iron accumulation, which will affect the iron status of the infant14. Of western women, 25 – 30% had no iron stores, 20% had 250mg and only 5% reached 400mg, short of the preferred 500mg before entering pregnancy. Women from developing countries15, in lower socio-economic groups, teenagers and multiparous women are at the highest risk of iron deficiency, due to their reduced dietary intakes or empty postpartum iron stores.

Epidemiological Studies

Maternal iron deficiency (Hb < 10 mg/dl) has been associated with increased rates of prematurity16, low birth weight and perinatal mortality17. High concentrations of haemoglobin were also associated with poor pregnancy outcomes, probably due to gestational hypertension in these women18. Low hematocrit women (37%) had twice the risk of a premature birth19, but the cause of the hematocrit was not examined. Low maternal haemoglobin, secondary to inadequate iron, was strongly related to high placental/birth weight ratio, and this anaemia may be predictive of long-term cardiovascular disease and hypertension20, but this relationship has yet to be elucidated.

Conclusion

Despite the facts that:

there remains a reluctance to introduce regional or national supplementation programmes23 in the UK. This in contrast to the USA, where the evidence for increased iron demand has been sufficient for the authorities to recommend supplementation with iron of 30 mg/d after 12 weeks of pregnancy24.

 

References

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