Maternal hemoglobin and hematocrit levels during pregnancy and childhood lung function and asthma. The Generation R Study

ObjectiveTo examine the associations of maternal hemoglobin and hematocrit levels during pregnancy with childhood lung function and asthma, and whether adverse pregnancy outcomes and atopic predisposition modify the associations. MethodsIn a population-based prospective cohort study among 3672 subjects, we measured maternal hemoglobin and hematocrit levels in early pregnancy, and lung function by spirometry and current asthma by questionnaire at age 10 years. ResultsHigher maternal hematocrit levels, both continuously and categorized into clinical cut-offs, were associated with lower forced expiratory flow at 75% of forced vital capacity (FEF75) in children (Z-score (95%CI): -0.04 (-0.07, -0.01), per increase of 1 SDS in hematocrit level; Z-score (95%CI) difference: -0.11 (-0.20, -0.03) compared with normal hematocrit levels, respectively), taking lifestyle and socio-economic factors into account. Adverse pregnancy outcomes and atopic predisposition did not modify the results. No associations of maternal hemoglobin and hematocrit with current asthma were observed. ConclusionHigher maternal hematocrit levels during pregnancy are associated with lower childhood lung function but not with risk of asthma. Adverse pregnancy outcomes and atopic predisposition do not modify these associations. Underlying mechanisms need to be further studied.