iron Deficiency in Pregnancy & Postpartum

Women are particularly at risk of iron deficiency due to blood loss during menstruation and the increased demand for iron during pregnancy.1 During pregnancy a woman’s iron requirements increase threefold to support the growth of the fetal-placental unit and increased red-cell mass.1 Meeting this demand requires a diet high in bioavailable iron during pregnancy, but also stored iron levels of at least 300 mg before pregnancy.2 Unfortunately, this pre-pregnancy level of iron stores is often not reached, with approximately 40% of women entering pregnancy with small body iron reserves and an unfavourable iron status.3 This leads to around 25% of pregnant women in Western societies having iron deficiency anaemia.3

The high risk of iron deficiency is also present postpartum. In one Danish study, 26% of women not taking iron supplements who had experienced a normal delivery were iron deficient one week after birth. 19% of the women in this study had iron deficiency anaemia one week after birth.4

Iron deficiency anaemia during pregnancy and postpartum can lead to serious consequences for both mother and child.5,6 It is therefore essential that iron deficiency is identified early and adequately treated before resulting in iron deficiency anaemia. 

iron requirements during pregnancy


The increased demand for iron is not spread evenly over the course of the pregnancy. In the first trimester iron requirements are partially met through the cessation of menstruation – saving 0.56 MG iron per day.2 In the second and third trimesters iron demand increases significantly.

Table 1. Daily iron requirements over the course of gestation2

Trimester iron Needs Per Day
1 ~0.8 mg
2 4 - 5 mg
3 > 6mg

Although iron absorption also increases during the second and third trimesters, to a maximum of 90% at 30 weeks, meeting the demand for iron through diet alone is difficult.2 Even with a diet high in bioavailable iron, overall absorption is only 3-4 mg/d.2

Iron requirements during pregnancy are illustrated in the figure below. In a 55 kg woman, approximately 450 mg of iron is required for the 35% increase in red blood cell mass that occurs during pregnancy.2 However, this iron requirement does not affect long-term iron balance because iron is recovered from the extra red blood cells and returned to the body’s stores at the end of pregnancy.2 Other iron losses during pregnancy include:

  • Iron needed by the foetus (approximately 270 mg for a 3.5 kg foetus)7
  • Obligatory iron losses through the mother’s skin, gut and urine (approximately 230 mg)2
  • Iron lost through maternal blood loss at delivery (approximately 200 mg of iron due to loss of approximately 400 mL of blood)7
  • Iron present in the placenta and umbilical cord (90 mg)2,7

These losses are partially off-set, however, by the absence of menstruation during pregnancy, so that the net iron demand of pregnancy is about 630 mg.7

Figure 1: Average iron requirement during pregnancy for a 55 kg woman2,7

Iron Deficiency Can Adversely Affect Outcomes

Iron deficiency anaemia is associated with negative outcomes during pregnancy, including increased risk of haemorrhage, sepsis, and maternal mortality.5 Women suffering from iron deficiency anaemia during the first two trimesters are twice as likely to deliver early, have three times the risk of having a low birth weight infant,8 and an increased risk of having an infant small for gestational age.3

Maternal iron Deficiency Can Impact on Infant Development 

Maternal iron deficiency anaemia can lead to premature birth or infants with a low birth weight.8 These infants are at risk of iron deficiency as they have missed part of an important stage of iron accrual – the third trimester.9 These iron stores are essential for appropriate development during the first 4-6 months of life as breast milk contains little iron,9 and the neonatal gut is too immature to regulate iron absorption until 6-9 months of age.10

Other conditions that put the neonate at risk of iron deficiency, even if carried to term, include maternal iron deficiency anaemia11 and diabetes during pregnancy.9

During the last trimester the brain starts a period of rapid development, which continues for the first two years of life, reaching 80-90% of its adult volume.10 The hippocampus, involved in learning, memory and cognition, is particularly susceptible to iron deficiency during the early stages of this growth spurt resulting in neurocognitive dysfunction.10 Some of these effects continue to adulthood, even after iron levels are restored.10

Impact of Postpartum iron Deficiency


Postpartum iron deficiency is common12 and anaemia caused by iron deficiency has been linked with the following consequences:

  • Increased risk of postnatal depression6
  • Increased prevalence of urinary tract infections13
  • Fatigue and exhaustion14
  • Insufficient milk syndrome15
  • Reduced breast milk quality16

Postnatal Depression

Postnatal depression can have a serious impact upon the health and emotional wellbeing of a new mother and her infant, as well as lead to ongoing cognitive effects.6 Low haemoglobin levels (≤12g/dL) seven days after a normal singleton delivery were shown to significantly correlate with self-reported depressive symptoms 28 days postpartum.6

Fatigue and exhaustion

Fatigue and exhaustion, beyond the normal tiredness expected of a mother with a newborn, are clinical symptoms of anaemia.14 Although detrimental in its own right, and a predictor of postnatal depression6, fatigue can also impact upon milk supply.14 One proposed mechanism by which fatigue impacts on milk production is that the mother is simply too tired to respond to the regular demands of a newborn, leading them to more frequently request that the infant is bottle-fed by someone else. This may disrupt the demand-supply relationship that is crucial to maintaining an adequate milk supply, increasing the mother’s likelihood of suffering from insufficient milk syndrome.15 For more information about identifying fatigue in your patients see our “Fatigue, exhaustion and tiredness” section.

Breastfeeding

The benefits of breastfeeding for both mother and infant are well known, but successful breastfeeding depends on a variety of factors. A study of first time mothers showed an association between anaemia and the development of insufficient milk syndrome, which in turn impacts on duration of full breastfeeding and age at weaning.15

One of the important roles of breast milk is the transfer of antibodies which help protect the infant against gastrointestinal and respiratory infections.16  Maternal anaemia is associated with reduced levels of antibodies and complement proteins, and differences in the fat and calorie content at different milk maturation stages.16

Women at Greater Risk


There are several factors that mean some women are at increased risk of iron deficiency during pregnancy and postpartum, outlined in Table 2 beneath.

Table 2.Factors increasing risk of iron deficiency in pregnancy and postpartum.

Pregnancy17 Postpartum
Iron deficiency prior to pregnancy Iron deficiency during pregnancy17
Multiple pregnancies Caesarean section (elective or emergency)18
Multipara Pre-pregnancy BMI > 2419
Poor socio-economic status Placenta previa18
Short recovery between pregnancies Hypertension18
After first trimester Bleeding after 28 weeks18
  Multipara18
  Premature or post-term delivery18
  Assisted delivery18
  High level of estimated blood loss during delivery18

Laboratory tests during pregnancy and postpartum


Breastfeeding

Testing for anaemia and iron deficiency during pregnancy, as well as in the postpartum period, has to take into consideration the haemodynamic changes occurring at these times. The normal increase in plasma volume during pregnancy leads to haemodilution, reducing haemoglobin concentration.2 Thus, the World Health Organisation (WHO) defines  anaemia in pregnancy as haemoglobin values <11 g/dL20 from a pre-pregnancy value of <12 g/dL1, whilst the US  Centers for Disease Control and Prevention adjust their recommendations in line with the changes seen in each trimester (see Table 3 below).21

Haemoglobin can be used as an indicator of iron status in pregnancy, because, if a haemoglobin test reveals anaemia,   ̴98% of the time it will be as a result of iron deficiency, and will be confirmed by the appropriate biomarker (see Table 3 below).3 However, haemoglobin has limited sensitivity for iron deficiency, since many women show normal haemoglobin levels despite having early or progressing iron deficiency.17

Table 3: Diagnosing iron deficiency without and with anaemia during pregnancy

Parameter Normal Range iron Deficiency iron Deficiency Anaemia
Haemoglobin (Hb) (g/dL) 12.0-1622 No decline in Hb levels observed in iron deficiency without anemia WHO: < 11.020
CDC21:
1st trimester < 11.0
2nd trimester < 10.5
3rd trimester < 11.0
Postpartum < 12.0
Serum ferritin (SF) (ng/mL) 15-15022 < 2022
> 50 if inflammation is present
< 1522
> 50 if inflammation is present
Transferrin saturation (TSAT)
(%)
15 - 4522 < 2022 < 2022
Serum transferrin receptor (sTfR)
(mg/L)
1.9 - 4.422

Markers of iron status such as serum iron, serum ferritin and total iron-binding capacity (TIBC), are affected by the changes of pregnancy.2  These effects can be quite pronounced, with a rise in TIBC to   ̴50% more than normal, and a decrease in serum ferritin concentration to   ̴50% of normal by midterm.2 Transferrin saturation (TSAT) is the percentage of occupied iron-binding sites on transferrin and is the ratio of serum iron and TIBC.23 Thus TSAT reflects the availability of iron in the plasma and is also affected by physiological changes during pregnancy.2

One test that seems to be unaffected by the normal changes of pregnancy is the measurement of the amount of serum transferrin receptors (sTfR). In both pregnant and non-pregnant women, high levels of sTfR indicates iron deficiency.3 In the first trimester of pregnancy, levels of sTfR are low due to inhibited erythopoiesis. As pregnancy progresses, levels of sTfR increase due to an increasing iron requirement for erythropoiesis, and can indicate iron deficiency.22 Iron-replete pregnant women, however, maintain lower levels of sTfR, similar to iron replete non-pregnant women.7

Postpartum

Blood loss during delivery in combination with pre-partum iron deficiency is a major cause of postpartum  anaemia,13 but assessing iron deficiency anaemia during this time can be difficult. The delivery of a baby is associated with an increased oxidative stress and inflammatory response.13 At the same time the patient’s hemodynamic status that changed during pregnancy is returning to its pre-pregnancy state.13 Serum ferritin levels have been shown to be particularly affected by delivery, and no longer reflect iron stores.17 In contrast, sTfR levels are not influenced by the inflammatory reaction and remain a good indicator of iron status in the early postpartum period.17

Treating iron deficiency in pregnancy and postpartum


For information on treatments for iron deficiency, please see “Treatment Options”.