The impact of low-dose aspirin on haemoglobin levels during pregnancy.

Abstract

Background: Low-dose aspirin, initiated between 12 and 28 weeks of gestation, is recommended for the prevention of preeclampsia, a major hypertensive complication of pregnancy. However, its influence on maternal haemoglobin levels—and its possible role in modifying anaemia risk, remains unclear. Anaemia continues to pose a significant burden in maternal health, contributing to increased morbidity and mortality. Aim: This study investigated the effect of low-dose aspirin on maternal haemoglobin levels and explored the association between haemoglobin changes and hypertensive disorders of pregnancy. Methods: This secondary analysis included 249 pregnant women selected from a larger randomised controlled trial, in which participants were randomised to receive 162 mg low-dose aspirin daily or standard care. Haemoglobin levels at enrolment were retrieved from trial records, while haemoglobin measurements at birth were extracted retrospectively from hospital maternity charts and the National Health Laboratory Service. Maternal outcomes, including hypertensive disorders of pregnancy, were analysed in relation to haemoglobin changes. Result: Of the total participants, 111 showed a decline in haemoglobin levels from enrolment to birth, while 138 demonstrated an increase. Repeated measures analysis of variance revealed a significant group-by-time interaction (p = 0.002, η² = 0.088) amongst those with declining haemoglobin. Participants in the low-dose aspirin group experienced a smaller decrease in haemoglobin (ΔHb = -0.902 g/dL) compared to the control group (ΔHb = -1.405 g/dL). Furthermore, a decline in haemoglobin was associated with higher odds of developing hypertensive disorders of pregnancy (odds ratio = 2.21 vs 0.45, p = 0.021). Within this subgroup, those receiving low-dose aspirin had a 76% lower risk of hypertensive disorders of pregnancy (relative risk = 0.24, 95% confidence interval [0.11–0.53], p < 0.001). Conclusion: Low-dose aspirin attenuated the decline in maternal haemoglobin levels, suggesting a novel haematological benefit beyond preeclampsia prevention. This therapeutic agent may offer value for integration into public health strategies aimed at improving maternal and fetal outcomes—particularly in low to middle-income countries, where anaemia is prevalent. A reduction in haemoglobin levels may also serve as an early predictor of hypertensive disorders of pregnancy.