Background and Aims: Maternal hemoglobin concentration during pregnancy is reported to be associated with various perinatal outcomes and may also be associated with infant development. This study aims to investigate the association between maternal hemoglobin levels during early or mid-pregnancy and sleep and developmental problems in 1-year-old infants. Methods: We used the data of 66,935 pregnant women who were participants of the Japan Environment and Children's Study, a nationwide cohort study in Japan, between 2011 and 2014. Maternal hemoglobin level was examined at recruitment (mean gestational age, 15.3 weeks; SD, 2.85 weeks; range, 6–22 weeks). Information on infant sleep and development at the age of 1 year was acquired using a questionnaire. Infant development was evaluated using the Ages and Stages Questionnaire (ASQ). Results: The mean (SD) maternal hemoglobin level was 12.0 (1.0) g/dl. Maternal hemoglobin levels were not associated with the majority of infant sleep and developmental outcomes. In the group with maternal hemoglobin <10.0 g/dl, the risk ratio (RR) for sleep at 22:00 or later was higher than that in the reference group with 11.0 g/dl ≤ hemoglobin < 14.0 g/dl (RR 1.12, 95% confidence interval = 1.00–1.25). In the analysis with maternal hemoglobin level as a continuous variable, both high and low hemoglobin levels were associated with a higher RR of a late bedtime. In addition, a low maternal hemoglobin level was associated with a higher RR for abnormal fine motor skills in the ASQ. Conclusion: Our results suggest that a low level of maternal hemoglobin during pregnancy is associated with late bedtime and abnormal fine motor skills in 1-year-old infants. Conversely, a high level of maternal hemoglobin may also be associated with the infant's late bedtime.
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