Background: The effects of low-level prenatal manganese (Mn) exposure on neonatal growth remain unclear. The level of fetal Mn that may be considered "safe" has never been examined.
Methods: A multicenter study including 1377 mother-infant pairs was conducted from 2008 through 2009 in Shanghai. Mn concentrations were determined for both the cord and maternal serum, as well as neonatal birth weight and birth length. The ponderal index (PI) was calculated as (birth weight g/birth length cm(3))×100, and a ponderal index ≥3.17 was defined as a high ponderal index (HPI).
Results: The median serum Mn concentration was 4.0μg/L in the cord blood, and was 2.8μg/L in maternal blood. Of 1377 infants, 135 (9.8%) had a HPI. After adjusting for potential confounders, cord serum Mn was not associated with birth weight. However, there was a linear relationship between the cord serum Mn and the birth length (adjusted ß=-0.5, 95% CI=-0.7 to -0.2, p<0.0001). Additionally, a nonlinear relationship was observed between the cord serum Mn and the ponderal index, and between the cord serum Mn and HPI. The ponderal index and the prevalence of HPI increased with Mn levels above 5.0μg/L (Log Mn ≥0.7). A high level of Mn in the cord (≥5.0μg/L) was associated with a higher ponderal index (adjusted ß=0.2, 95% CI=0.1 to 0.2, p<0.001) and a high risk of HPI (adjusted OR=3.3, 95% CI=1.8-6.0, p<0.001).
Conclusions: Higher prenatal Mn exposure, even at a low level, is associated with a higher prevalence of HPI in a nonlinear pattern. Cord serum Mn levels less than 5.0μg/L may be considered safe with respect to neonatal ponderal index assessment.
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