Haemoglobin concentration in early pregnancy predicts neonatal morbidity, mortality

Anaemia and relative erythrocytosis during early pregnancy are independently associated with neonatal morbidity and mortality, a study has found.

Investigators in Ontario, Canada, conducted a population-based, retrospective cohort study comprising women aged 18‒50 years with a singleton birth between 2007 and 2023 and haemoglobin measurement at 2‒12 weeks’ gestation. Overall, 1,100,341 live births were included.

Using restricted cubic splines, the nonlinear relation between early pregnancy haemoglobin concentration and severe neonatal morbidity and mortality (SNM-M) in a high-income setting was analysed in 1-g/L increment, with 125 g/L as reference.

A validated composite measure of SNM-M (major neonatal conditions and critical interventions) up to 27 days after birth served as the primary endpoint. The investigators calculated the relative risks (RRs), with adjustment for maternal demographic characteristics and chronic conditions.

Early pregnancy haemoglobin concentration showed a U-shaped association with SNM-M. For instance, the adjusted (a)RR for SNM-M was 1.08 (95 percent confidence interval [CI], 1.04‒1.11) at a haemoglobin concentration of 105 g/L and 1.17 (95 percent CI, 1.10‒1.25) at 90 g/L relative to a haemoglobin value of 125 g/L and a corresponding SNM-M rate of 6.7 percent.

Furthermore, a haemoglobin concentration of 135 g/L correlated with a 5-percent risk for SNM-M (aRR, 1.05, 95 percent CI, 1.03‒1.07), while a concentration of 150 g/L resulted in a 20-percent increased risk (aRR, 1.20, 95 percent CI, 1.16‒1.24).

“Randomized clinical trials should evaluate the effect of iron therapy on maternal and perinatal outcomes by degree of haemoglobin correction,” the investigators said.

The study was limited by the unknown iron replacement status before and during pregnancy and by residual confounding which may influence observed associations.