BACKGROUND AND PURPOSE:

• Many studies use hemoglobin levels later in pregnancy when assessing the relationship between anemia and adverse perinatal outcomes
• Ray et al. (BJOG, 2020) evaluated the association between early maternal hemoglobin concentration and severe maternal morbidity or maternal mortality

METHODS:

• Population-based cohort study
• Population
  • Pregnant women
  • Routine outpatient hemoglobin measured between 2 and 16 weeks
• Study design
  • The relationship between early-pregnancy outpatient blood hemoglobin concentration and each study outcome was expressed as adjusted relative risks (aRR) and absolute risk differences (aRD)
  • Mode of birth, BMI and iron supplementation were added to the model
  • Normal hemoglobin reference range: 125 to 129 g/L
• Primary outcome
  • Severe maternal morbidity composite or maternal mortality, from 23 weeks gestation to 42 days postpartum
  • Severe morbidity composite comprises approximately 40 morbidity measures (ante-, intra- and postpartum)

RESULTS:

• 737,393 births
  • Mean (SD) hemoglobin concentration: 126.9 (9.3) g/L
• Overall severe maternal morbidity or deaths: 1.8%

Pregnancies with lower hemoglobin levels were at higher risk of the primary outcome vs normal reference range

Risk increased with lower hemoglobin levels

• 120 to 124 g/L
  • aRR 1.07 (95% CI, 1.02 to 1.13)
  • aRD 0.09% (95% CI, 0.01 to 0.18)
• 105 to 109 g/L
  • aRR 1.31 (95% CI, 1.17 to 1.46)
  • aRD 0.47% (95% CI, 0.24 to 0.69)
• <90 g/L
  • aRR 4.53 (95% CI, 3.59 to 5.72)
  • aRD 5.94% (95% CI, 4.12 to 7.76)

Transfusion Risk

• 0.8% of women required red cell transfusion
• Risk of requiring red cell transfusion was significantly higher at all hemoglobin concentrations <125 to 129 g/L
  • Peak adverse perinatal outcomes occurred at a hemoglobin level <90 g/L
  • aRR 11.82 (95% CI, 9.30 to 15.03)

CONCLUSION:

• In pregnant women, risk of severe maternal morbidity, death, and red cell transfusion increases with decreasing hemoglobin levels with a peak at hemoglobin level <90 g/L
• The authors state

…the current findings provide precise haemoglobin thresholds to guide clinicians in their assessment of a woman’s future risk of unfavourable outcomes, including who may benefit from preventative interventions

An RCT comparing low dose versus high dose iron therapy initiated in early pregnancy might be warranted at different haemoglobin thresholds, with the highest potential population level impact likely among women whose haemoglobin concentration is <110 g/l

Learn More – Primary Sources:

Haemoglobin levels in early pregnancy and severe maternal morbidity: population‐based cohort study

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