Non-Invasive Measurement of Serum Haemoglobin for the Detection of Postpartum Anaemia: A Prospective Observational Study

Background/Objective: The primary aim of this study was to establish a clinically relevant cut-off for detecting postpartum anaemia using non-invasive haemoglobin measurement, and to compare the non-invasive method with laboratory haemoglobin testing. This study was conducted as a prospective observational study at a single centre. Pregnant women giving birth vaginally or by caesarean birth at a university hospital were included in this study. Methods: We measured haemoglobin by non-invasive and laboratory means at delivery room discharge and after childbirth in the operation room. We then calculated a clinically relevant cut-off for detecting postpartum anaemia using the non-invasive measurement method. The main outcomes were the invasively and non-invasively measurements of haemoglobin and the correlation between the two measurements. Results: In total, 466 complete measurement pairs from 323 women were included, and 179 (38.4%) laboratory measurements were found to be anaemic (haemoglobin value < 11 g dL−1). Maximising specificity while maintaining a minimum sensitivity of 80%, we identified a cut-off of 13.75 g dL−1, which achieved a sensitivity of 81.0% and a specificity of 54.7%. The NPV at this threshold was 82.2%, while the PPV was 52.7%. The mean difference between measurements was found to be +2.3 g dL−1 (CI 95% 2.16 to 2.43). Conclusions: Non-invasive haemoglobin measurement did not sufficiently detect anaemia compared to laboratory measurement values in the setting of early postpartum women, even after adjusting for bias. However, the proposed cut-off could potentially aid healthcare providers in low-resource situations.