Abstract
Background: Previous results of prenatal mercury exposure have shown moderate levels in Spanish newborns -mainly due to elevated fish consumption-, and have also shown a possible association with neonatal anthropometry. Moreover, there are scarce studies relating moderate chronic mercury exposure with other reproductive outcomes, such as gestational length and placental weight, which could play a critical role in the understanding of biological mechanisms involved in fetal growth. Aim: To assess the association between prenatal mercury exposure and placental weight and the length of gestation in a multicenter population based birth cohort. Methods: A total of 2506 children born between 2004 and 2008 in four cohorts (Valencia, Sabadell, Asturias, and Gipuzkoa) within the Spanish INMA project (Childhood and the Environment: www.proyectoinma.org). Cord blood total mercury was determined in 1886 samples. Cohort specific linear, logistic, and Cox models were adjusted to evaluate the association between mercury exposure and placental weight, placental to fetal weights ratio, preterm, and gestational length, respectively. Non-spontaneous labour was taken to be censoring in the survival analysis. Final estimates were obtained using meta-analysis, correcting for heterogeneity when appropriate. All models were adjusted for fish intake species and other potential confounders obtained through questionnaires. Results: A doubling in total mercury levels was associated with 7.6 grams decrease in placental weight (95% CI: -13.6, -1.7). This result was homogeneous among cohorts and showed a linear pattern. Placental to fetal weights ratio showed also an inverse nearly significant relation to mercury (% change: -0.7; 95% CI: -1.5, 0.1). Duration of pregnancy was not related to mercury concentration, although a heterogeneous pattern was observed among cohorts (I2=58%). Conclusions: These results suggest that prenatal exposure to mercury may affect placental growth, a marker of placental functional efficiency.
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