Effects of Lead and Other Metals on Pregnancy Outcomes

Abstract

Societyʼs industrialization and constant need for new products and components have increased the number and concentration of toxic substances that women are exposed to in their environment and workplaces. For decades, metal toxicity has remained a topic of concern for its effects on pregnant women. Although the level of exposure to many toxic metals has decreased sharply, research has revealed the impact of low-level metal exposure on different aspects of pregnancy. Lead is one of the toxic metals for which the effects on the human reproductive system have been intensively studied. The US Centers for Disease Control and Prevention have recommended a blood lead level of < 5.0 mg/dl as a screening action guideline in pregnant women. However, many studies have shown the adverse effects of lead on several human reproductive outcomes, such as low birth weight, preterm rupture of the membrane, and pregnancy hypertension, even at the ʻacceptableʼ level of blood lead. This supports a reappraisal of the ʻsafeʼ or ʻacceptableʼ level.We aimed to conduct a review of our several-year-long longitudinal study on prenatal metal exposure and pregnancy outcomes.Key words: lead, manganese, metal, women, pregnancy Pregnancy and metal exposurePregnancy is an important and unique period of a womanʼs life in which there is high sensitivity to toxic substances. Women can be exposed to metal direct in their workplaces, polluted environments, and/or exposed indirectly by relatives who bring contaminated work instruments or work-clothes home. In addition, there is a special route of exposure during pregnancy, endogenously, as many metals can mobilize from accumulated organs, such as bones, to the bloodstream several years after a woman underwent external exposure. Since the placenta only partially prevents metal diffusion 1) , metals can cross the fetal membrane and potentially harm fetuses as well. Since no level has been proven safe during pregnancy for many toxic metals 2) , scientistsʼ focus has shifted from high-dose toxicity and clinically symptomatic individuals to lowerdose exposures that may cause subclinical problems.In a longitudinal and multicenter study, originally consisting of 364 women at the first trimester of pregnancy (gestational age of 8-12 weeks), we collected and measured metal concentrations in maternal whole-blood samples, one for each trimester (3 samples), and umbilical cord blood samples at the time of delivery. The full follow-up was completed for 224 mothers until delivery. The survey participants were non-smokers with singleton pregnancies, who were free from chronic conditions. Metal and pregnancy outcomesSo far, in three separate studies based on the cohort study data, we have showed adverse pregnancy outcomes induced by blood metals at relatively low levels. Blood metals at the first trimester of pregnancy showed more significant 458 Lecture Notes