delayed neurodevelopment (7–9) and low birth weight (10–
12). Upon the placement of dental amalgam, the urinary
mercury concentrations increase approximately ninefold
within the first week, reaching a peak concentration of
approximately 8 lg of mercury for a 24-hour urine sample.
Recommendation to abandon mercury-containing amalgam
fillings during pregnancy is not without potential risks.
Resin-based dental filling materials, the most common
alternative to mercury-containing dental amalgams, can
leach estrogen-like molecules that in animal models have
been associated with an abnormal number of chromosomes
in eggs, fetal loss, and other adverse pregnancy outcomes (13,
14). Several countries have expressed the need for better
epidemiologic research to establish evidence-based guide-
lines on the use of dental filling materials during pregnancy.
The goal of this study was to determine the potential
associations between mercury-containing dental fillings
placed during pregnancy and risk of low-birth-weight
infants. A secondary aim was to evaluate whether resin-
based materials affected birth weight.