Prenatal exposure to mercury and precocious puberty: a prospective birth cohort study

STUDY QUESTION: Is in utero exposure to mercury associated with the risk of precocious puberty? SUMMARY ANSWER: Prenatal exposure to high levels of mercury was associated with increased risk of precocious puberty, which was strengthened by concomitant maternal cardiometabolic conditions and adverse birth outcomes. WHAT IS KNOWN ALREADY: The developing fetus is sensitive to mercury, a well-known endocrine disruptor which impacts the endocrine and reproductive system. STUDY DESIGN, SIZE, DURATION: This study included 1512 mother-child pairs from the Boston Birth Cohort, a longitudinal cohort which recruited at birth and followed prospectively up to 21 years of age. PARTICIPANTS/MATERIALS, SETTING, METHODS: Mother-child pairs, from a predominantly urban minority population, were enrolled from 2002 to 2013. Prenatal exposure was assessed by maternal mercury concentration in red blood cells (RBCs) collected at I-3 days after delivery. Precocious puberty was defined based on International Classification of Disease codes. Cox proportional hazards models were applied to the association between maternal mercury concentrations and the risk of precocious puberty. MAIN RESULTS AND THE ROLE OF CHANCE: The median (interquartile range) of maternal mercury concentrations among children with and without precocious puberty were 3.4 (1.9-4.6) mu g/l and 2.0 (1.0-3.7) mu g/l, respectively. Compared to those in the lowest tertile for mercury, the highest tertile was associated with increased risk of precocious puberty, with an adjusted hazard ratio (HR) of 2.41, 95% CI: 1.16-5.03. In addition, concomitant maternal cardiometabolic conditions and adverse birth outcomes strengthened the effects of mercury on the risk of precocious puberty. The highest risk of precocious puberty was observed among children who had adverse birth outcomes and whose mothers had high RBC-mercury concentrations along with cardiometabolic conditions, with an HR of 4.76 (95% CI: 1.66-13.60) compared to children with favorable profiles of all three risk factors. LIMITATIONS, REASONS FOR CAUTION: Precocious puberty was defined based on medical records, not on a direct assessment, which may have led to underdiagnosis and the inability to make a subclassification. The study included a predominately urban, low-income, minority population and as such our findings may not be widely generalizable. WIDER IMPLICATIONS OF THE FINDINGS: Prenatal Hg exposure was associated with an increased risk of precocious puberty. This risk was strengthened by concomitant maternal cardiometabolic conditions during pregnancy and adverse birth outcomes.