Chinese researchers find link between prenatal rare earth exposure and low birthweight

A study of nearly 4,900 pregnant women in China has found an association between prenatal exposure to rare earth elements and an increased risk of low birthweight, with some individual elements and combinations showing substantially higher odds.

Researchers led by Wang Youjie at Huazhong University of Science and Technology analyzed urine samples from 4,891 women who gave birth at Wuhan Maternal and Child Health Hospital between 2012 and 2014. The team measured 13 rare earth elements, including cerium, ytterbium and lanthanum, and examined whether exposure was associated with birth outcomes.

The researchers found that a 1 microgram-per-gram increase in the concentration of an individual rare earth element was associated with a 25.6% to 51.4% increase in the odds of low birthweight after accounting for factors including maternal age and body mass index.

Cerium emerges as the main contributor

The researchers also looked at exposure to all 13 elements simultaneously using a weighted quantile sum regression model, which is designed to assess the combined effects of chemical mixtures, the South China Morning Post reported.

The resulting odds ratio was 2.004, meaning the modeled mixture was associated with roughly twice the odds of low birthweight. In some analyses involving individual elements or combinations of rare earths, the odds ratios exceeded 3 or even 4. Cerium was the strongest contributor to the mixture, accounting for almost half of its estimated harmful weight.

The study population nevertheless had a relatively low measured incidence of low birthweight, at 0.8%. Meanwhile, 7.9% of newborns were classified as small for their gestational age. Importantly, the researchers noted that they did not find a significant association between rare earth exposure and being small for gestational age.

The findings therefore point specifically to an association with birthweight rather than demonstrating that rare earth exposure causes restricted fetal growth.

The study has important limitations

Rare earth elements are increasingly important to industries ranging from electronics and renewable energy to advanced defense systems. Their mining and processing can also release metals and other contaminants into surrounding environments.

The new study adds another potential health concern, but the researchers themselves caution against interpreting the results as proof of causation. One of the main limitations is that exposure was assessed using a single urine sample. A single measurement may not accurately capture a mother’s exposure throughout pregnancy, particularly because concentrations of some substances can change over time.

The authors say the findings need to be confirmed through larger and more extensive prospective studies, which can be particularly important because the research examines an observational association. Even though the analysis adjusted for several potential confounding factors, other unmeasured factors could still contribute to the observed relationship.

Furthermore, the study does not establish that China’s rare earth industry caused the observed birthweight associations, nor does it determine which specific environmental sources were responsible for the women’s exposure. Instead, it provides evidence that prenatal exposure to mixtures of rare earth elements deserves further investigation. Next, the researchers plan to do broader studies that can track exposure throughout pregnancy and examine whether the associations can be replicated across different populations.