Urinary levels of toxic metals and pregnancy and newborn outcomes: biomonitoring of the IoMum cohort

Abstract

Introduction: Pregnant women are subject to exposure to various toxic metals, which can have a significant impact on both maternal and fetal health, particularly exposure occurring during the first trimester of pregnancy. This period represents a time window of unique vulnerability, in which exposure can dramatically affect the health of the mother and newborn both on the short and on the long-term. Aims: To evaluate the association between the level of exposure of pregnant women in the IoMum cohort to four toxic metals - bismuth (Bi), thallium (Tl), nickel (Ni), and antimony (Sb) - with sociodemographic characteristics of the study sample, pregnancy outcomes, and anthropometric parameters of the newborn. Methods: This was a prospective study based on the IoMum cohort (trial registration #NCT04010708, ethical approval #292/17). Pregnant women invited to participate in this study were those who underwent routine first-trimester ultrasounds from April 2018 to April 2019 at Centro Hospitalar São João. All women with gestational age between 10 weeks and 13 weeks plus 6 days, confirmed foetal vitality and who signed the informed consent were included in the study. Spot urine samples from eligible participants were analyzed using the ICP-MS technique to quantify urinary concentrations of metals. Then, using non-parametric statistical tests, the possible association between exposure to Bi, Tl, Ni and Sb, and sociodemographic variables of the mother, pregnancy outcomes, and anthropometric parameters of the newborn was evaluated. Results: The study sample corresponded to the number of collected urines (n=349). The urinary metal concentrations of the studied metals were, in µg/L: Bi 0.02 , Tl 0.02, Ni 4.3 and Sb 0.04. The detection rates of each metal (defined as the percentage of samples with an urinary metal concentration ≥LOD) were: 10.9% for Bi, 47.6% for Tl, 98.3% for Ni and 16.1% for Sb. Median urinary Tl and Bi excretion was associated with residence area, with higher values for pregnant women residing in Valongo, compared to other municipalities. Increasing maternal age was associated with higher urinary excretions of Bi, Sb, and Tl. Regarding pre-pregnancy body mass index, Bi, Ni, and Sb urinary excretion consistently decreased from normal weight to obese women. Occupation as a health professional was associated with higher urinary excretion of Bi and Ni. Occupations categorized as "high exposure" - which included health professionals, aestheticians, hairdressing professionals, warehouse operators, industry workers, cooks, and housekeeping professionals - were also associated with higher excretions of all the metals. In relation to dietary exposure, urinary Tl excretion increased consistently with the frequency of fish consumption. In addition, urinary Tl excretion consistently increased with increasing anthropometric categories of birth weight, birth head circumference, and birth length Also, urinary Ni tended to show higher levels of excretion for adequate categories of birth head circumference and birth length. Finally, the median for urinary Ni excretion was much higher in women who had delivery complications and in women who have had a baby with malformations. Conclusion: The present study showed that some professions may increase the exposure of pregnant women to the studied toxic metals. Despite this, the levels of exposure are not of concern regarding possible impact on maternal or newborn health.