Anaemia in pregnancy poses global health risks, yet the impact of specific haemoglobin levels remains uncertain. This study investigated the association between maternal haemoglobin concentrations during pregnancy and the risk of adverse maternal and neonatal outcomes. Recently published in The Lancet Haematology, the findings support revising current haemoglobin concentration cutoffs during pregnancy to account for both low and high levels, given the association of both with adverse neonatal and maternal outcomes.
Anaemia in pregnancy is a global health problem with associated maternal and neonatal morbidity and mortality. The global prevalence of anaemia among pregnant women aged 15-49 was estimated at 36.5% in 2019, based on the World Health Organization (WHO) definition of less than 110 g/L haemoglobin. However, there is little evidence that specific haemoglobin thresholds can predict health risks for the mother and her child. To address this gap, this study aimed to investigate the association between maternal haemoglobin concentrations during pregnancy and the risk of adverse maternal and neonatal outcomes. Notably, this study is the first to use high-quality individual-level data from five multinational sites to quantify the relative risk of adverse maternal and neonatal outcomes according to haemoglobin concentrations during pregnancy when compared with the current trimester-specific WHO haemoglobin cutoffs.
The prospective, observational, multinational INTERBIO-21st foetal study was conducted at maternity units in Brazil, Kenya, Pakistan, South Africa, and the UK, enrolling pregnant women (aged ≥18 years, BMI <35 kg/m2, natural conception, and singleton pregnancy) who initiated antenatal care before 14 weeks gestation. At each 5±1 weekly visit until delivery, information was collected about the pregnancy, as well as the results of blood tests taken as part of routine antenatal care, including haemoglobin values. The outcome measures were maternal (gestational diabetes, pregnancy-induced hypertension, and preterm premature rupture of membranes) and neonatal outcomes (small for gestational age, preterm birth, and acute respiratory distress syndrome).
This study included 2,069 women who had at least one routinely haemoglobin concentration measured at 14-40 weeks gestation between 2012 and 2019, resulting in 4,690 haemoglobin measurements for the analysis. Overall, compared with a haemoglobin cutoff of 110 g/L, the risk was increased more than two-fold for pregnancy-induced hypertension at haemoglobin concentrations of ≥170 g/L (risk ratio [RR]: 2.29, [95%CI: 1.19-4.39]), for preterm birth at haemoglobin concentrations of 70 g/L (RR: 2.04 [95%CI: 1.20-3.48]) and 165 g/L (RR 2.06 [95%CI: 1.41-3.02]), and for acute respiratory distress syndrome at haemoglobin concentrations of 165 g/L (RR 2.84 [95% CI]: 1.51-5.35). Similarly, specific values above and below the trimester-specific cutoffs for maternal anaemia (<110 g/L, 105 g/L, and 110 g/L for the first, second, and third trimesters of pregnancy, respectively) showed association with increased risks of adverse maternal and neonatal outcomes. Notably, even when comorbidities such as cancer, thalassemia, sickle cell disease, and HIV were excluded, the overall results remained largely unchanged. Moreover, adjusting for iron supplementation did not significantly impact the results.
These data suggest that the current WHO haemoglobin cutoffs are associated with a reduced risk of adverse maternal and neonatal outcomes. Importantly, the findings support revising current haemoglobin concentration cutoffs during pregnancy to account for both low and high levels, given the association of both with adverse neonatal and maternal outcomes.
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