PROTECT Study finds that among metals, maternal blood lead concentrations were strongly associated with increased risk of preterm birth

PROTECT explores how environmental exposures during pregnancy may impact preterm birth risk, specifically studying a Puerto Rican cohort due to higher levels of preterm birth compared to the U.S. mainland. In this instance, pregnant women in this cohort had relatively low blood lead (Pb) concentrations when compared to the general US population. However, despite the lower concentrations, analysis revealed that maternal blood lead was the most strongly associated with increased risk of preterm birth of all the metals assessed. The results provide evidence that even very low lead exposure, indicated by blood lead levels well below current reference levels, may be associated with preterm birth. Additionally, they found that elevated levels of essential metals manganese and zinc during pregnancy may also adversely affect birth outcomes.

This study, conducted by PROTECT Project 1, used data collected from 812 pregnant women participating in the ongoing prospective PROTECT cohort. Each woman participated in up to three study visits at approximately 18, 22, and 26 weeks of gestation. Blood samples were collected from women at the first and third visits. All the birth outcome data were abstracted from medical records. Within preterm birth studies, gestational age is commonly used to describe how far along the pregnancy is in terms of weeks. Preterm birth occurs when a baby is delivered before the start of the 37th week of pregnancy, which can often cause complicated medical problems.

Lead and mercury are considered a non-essential metal and are toxic to human body, even in very low amounts. In contrast, essential metals such as manganese and zinc play a key role in physiological processes in the human body. However, the essential metals can also be toxic to the human body at high concentrations despite their benefits. Additionally, both types of metals can be labeled as environmental toxicants at high concentrations in our ecosystems. As humans are continuously exposed to a mixture of environmental toxicants, there is a pressing need to study the relationship of exposures both individually and as mixtures. While most studies on metals have assessed metal exposures individually rather than in combination, only a few have explored metal mixtures in relation to adverse birth outcomes. This study measured a large range of both essential and non-essential metals while also investigating the effects of metals on adverse birth outcomes both individually and as mixtures.

“These findings provide further support for the need to reduce lead exposure to the greatest extent possible among vulnerable populations, including pregnant women and children,” explains author Pahriya Ashrap. “Therefore, we advise pregnant women to try to avoid common sources of lead exposure, including lead paint in older homes, house dust, contaminated garden soil, certain cosmetics, and lead-glazed ceramics.”

PROTECT explores how environmental exposures during pregnancy may impact adverse birth outcomes such as preterm birth risk. This study has gathered important information on levels of prenatal exposure to metals among pregnant women in Puerto Rico and given insight into relationships between prenatal metals exposure and risk of preterm birth. “By identifying modifiable environmental risk factors for adverse birth outcomes (such as metals), this work supports contaminant remediation and other exposure reduction strategies in an effort to reduce rates of preterm birth and other adverse health effects, resulting in an overall positive impact on public health,” states Pahriya.

Fig. 2. Preterm birth (overall) odds ratio (95% confidence interval) associated with tertiles of geometric average exposureab Models were adjusted for maternal age, maternal education, pre-pregnancy BMI, and exposure to secondhand smoking. aReferent levels were set at tertile 2 for essential metals (Cu, Mn, Zn). bReferent levels were set at tertile 1 for non-essential metals (Hg, Pb), and environmental risk score (ERS). △ Individual metals that were selected from elastic net models to compose ERS.