Association between maternal hemoglobin concentration and placental
weight to birthweight ratio: the Japan Environment and Children’s Study
(JECS)
Abstract
Objective: To evaluate the associations between maternal hemoglobin
concentration during pregnancy and placental weight, birthweight, and
placental weight to birthweight ratio (PW/BW ratio). Design: A cohort
study. Setting: Data from the Japan Environment and Children’s Study
(JECS). Population: 83 354 singletons born at 28 to 41 weeks of
gestational age and their mothers. Methods: The associations between
maternal hemoglobin concentration and placental weight, birthweight, and
PW/BW ratio were assessed by applying regression analyses with
restricted cubic splines. Main outcome measures: Placental weight,
birthweight, and PW/BW ratio. Results: Adjusted placental weight and
birthweight decreased as hemoglobin concentration increased. The
decrease in placental weight was more marked when the hemoglobin
concentration was below12 g/dl; however, the decrease in birthweight was
steeper when the hemoglobin concentration was above 12 g/dl. Analysis
showed that the PW/BW ratio followed decreasing trend as the hemoglobin
concentration increased to 12 g/dl, at which point the ratio changed
into increasing trend. Conclusions: We found that placental weight was
higher in women with low hemoglobin level during pregnancy than women
with normal or elevated hemoglobin level while birthweight of women with
elevated hemoglobin level is lower than that of women with normal
hemoglobin level. As a result, a U-shaped relationship was found between
maternal hemoglobin concentration and PW/BW ratio. Funding: The Japan
Environment and Children’s Study was funded by the Ministry of the
Environment, Japan. Key words: anemia during pregnancy, hemoglobin,
Japan Environment and Children’s Study, JECS, placental weight