Anaemia (in pregnancy)

ANAEMIA IN PREGNANCY

Over 80-90% of anaemia in pregnancy in the UK is due to iron deficiency.

Definition and diagnostic cut-offs

• in the UK, anaemia in pregnancy is defined as haemoglobin < 110 g/L in the first trimester, < 105 g/L in the second and third trimesters, and < 100 g/L postpartum (1,2)
• World Health Organisation defines anaemia in pregnancy as haemoglobin < 110 g/L across all trimesters (at sea level)

Aetiology and risk factors

• anaemia in pregnancy is more common in patients who are already anaemic or iron-depleted prior to conception
• risk factors include pre-existing menorrhagia, poor dietary intake, short inter-pregnancy interval (< 1 year), high parity, multiple gestation, and inherited haemoglobinopathies (1,4)

Screening and diagnosis

• full blood count should be offered routinely at booking and at 28 weeks gestation, with an additional check at 20-24 weeks for multiple gestations (1,2)
• routine unselected serum ferritin screening is not recommended for all pregnancies (2)
• serum ferritin should be measured early in pregnancy for non-anaemic women at high risk of iron depletion (2)
• serum ferritin < 30 micrograms/L indicates non-anaemic iron deficiency and warrants early oral iron supplementation (2)
• serum ferritin < 15 micrograms/L indicates severe iron depletion (2)
• a microcytic hypochromic blood film should prompt iron-replacement therapy once haemoglobinopathies are excluded (2,4)

Management of iron deficiency anaemia

Oral iron therapy

• first-line treatment for mild iron deficiency anaemia (2)
• modern UK guidelines recommend 65 mg to 100 mg elemental iron daily, such as ferrous fumarate 210 mg once daily or ferrous sulphate 200 mg once daily (2)
• alternate-day dosing or lower daily dosing can be used to improve gastrointestinal tolerance (2)
• oral iron should be taken on an empty stomach with a source of vitamin C, avoiding tea, coffee, dairy, or antacids (2)
• monitoring requires a repeat full blood count at 2-4 weeks, where an adequate response is an increase in haemoglobin of >= 10 g/L (2)
• treatment should continue for 3 months post-correction and at least until 6 weeks postpartum (2)

Parenteral (intravenous) iron

• indicated from the second trimester onwards if there is oral iron intolerance, lack of response to a 2-week oral trial, or late gestation (> 34 weeks) with significant anaemia requiring rapid correction (2)
• systematic review evidence demonstrates that intravenous iron significantly increases maternal haemoglobin and ferritin, increases neonatal ferritin stores, and reduces delivery blood transfusions by 37% (RR 0.63) with an 89% reduction in gastrointestinal adverse events compared to oral iron (3)

Referral and transfusion

• urgent secondary care referral is indicated if haemoglobin < 70 g/L, if severe symptoms are present, or at late gestation (> 34 weeks) (2)
• blood transfusion should be restricted to cases with active bleeding, imminent hemodynamic compromise, or severe symptoms near delivery (2)

Folate deficiency anaemia

• second most common cause of anaemia in pregnancy (1)
• causes macrocytosis which can mask co-existing microcytic iron deficiency (1)
• treated with oral folic acid 5 mg daily (1)

Notes:

• physiological anaemia occurs because plasma volume expands to a greater extent than red cell mass, reducing blood viscosity (1,5)
• lowest perinatal mortality and optimal birth weight are associated with a lowest recorded maternal haemoglobin concentration between 90-110 g/L (9.0-11.0 g/dL) (5,6)
• in well-nourished populations, a fall in haemoglobin to between 90-110 g/L often indicates healthy plasma volume expansion rather than true iron deficiency (5)

Reference:

1. National Institute for Health and Care Excellence (NICE). Antenatal care (NICE Guideline NG201). Published August 2021 (Last updated 2024).
2. Pavord S, Daru J, Prasannan N, et al. UK guidelines on the management of iron deficiency in pregnancy. Br J Haematol. 2020;188(6):819-830.
3. Sales SK, Rajprohat S, Simon L, et al. Intravenous vs Oral Iron for Treating Iron Deficiency Anemia in Pregnancy: A Systematic Review and Meta-Analysis. JAMA Netw Open. 2026;9(9):e2630657.
4. Barroso F, Allard S, Kahan BC, et al. Prevalence of maternal anaemia and its predictors: a multi-centre study. Eur J Obstet Gynecol Reprod Biol. 2011;159(1):99-105.
5. Little MP, Brocard P, Elliott P, Steer PJ. Hemoglobin concentration in pregnancy and perinatal mortality: a London-based cohort study. Am J Obstet Gynecol. 2005;193(1):220-226.
6. Steer PJ. Maternal hemoglobin concentration and birth weight. Am J Clin Nutr. 2000;71(5 Suppl):1285S-1287S.