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Introduction: Placental function is essential for fetal development, but it may be susceptible to malnutrition and environmental stressors.

Objective: To assess the impact of toxic and essential trace elements in placenta on placental function.

Methods: Toxic metals (cadmium, lead, mercury, cobalt) and essential elements (copper, manganese, zinc, selenium) were measured in placenta of 406 pregnant women in northern Sweden using ICP-MS. Placental weight and birth weight were obtained from hospital records and fetoplacental weight ratio was used to estimate placental efficiency. Placental relative telomere length (TL) and mitochondrial DNA copy number (mtDNAcn) were determined by quantitative PCR (n = 285). Single exposure-outcome associations were evaluated using linear or spline regression, and joint associations and interactions with Bayesian kernel machine regression (BKMR), all adjusted for sex, maternal smoking, and age or BMI.

Results: Median cadmium, mercury, lead, cobalt, copper, manganese, zinc, and selenium concentrations in placenta were 3.2, 1.8, 4.3, 2.3, 1058, 66, 10626, and 166 μg/kg, respectively. In the adjusted regression, selenium (>147 μg/kg) was inversely associated with placental weight (B: −158; 95 % CI: −246, −71, per doubling), as was lead at low selenium (B: −23.6; 95 % CI: −43.2, −4.0, per doubling). Manganese was positively associated with placental weight (B: 41; 95 % CI: 5.9, 77, per doubling) and inversely associated with placental efficiency (B: −0.01; 95 % CI: −0.019, −0.004, per doubling). Cobalt was inversely associated with mtDNAcn (B: −11; 95 % CI: −20, −0.018, per doubling), whereas all essential elements were positively associated with mtDNAcn, individually and joint.

Conclusion: Among the toxic metals, lead appeared to negatively impact placental weight and cobalt decreased placental mtDNAcn. Joint essential element concentrations increased placental mtDNAcn. Manganese also appeared to increase placental weight, but not birth weight. The inverse association of selenium with placental weight may reflect increased transport of selenium to the fetus in late gestation.