Metals exposure and risk of small-for-gestational age birth in a Canadian birth cohort: The MIREC study (Lay summary)

Thomas S, Arbuckle TE, Fisher M, Fraser WD, Ettinger AS, King W. Environmental Research. 2015 Jul;140:430-9. doi: 10.1016/j.envres.2015.04.018.

Lead, mercury, cadmium, and arsenic are some of the most common environmental metals to which Canadians are exposed. The effect of exposure to current low levels of these metals on “small-for-gestational-age”, or SGA, is unknown. SGA infants weigh less than 90% of infants born at the same gestational age

In this study, researchers at Queen’s University, in collaboration with Health Canada, investigated the potential relationships between exposure to lead, mercury, cadmium, and arsenic during pregnancy, and the risk of the infant being SGA at birth. They measured the levels of these environmental contaminants in first and third trimester blood samples from 1,835 pregnant women participating in the MIREC Study. Levels of arsenic in first trimester urine were also measured. Also considered in the analysis were other important factors that could influence the analysis and study results; these factors included maternal age, parity, pre-pregnancy body mass index or BMI (an indicator of your weight-to-height ratio), and smoking. [Parity is the number of times a woman has given birth. Gestational age is a measure of how far along the pregnancy is in weeks, starting from the first day of the woman’s last menstrual period to the date of birth.]

The researchers found no association between the levels of lead, cadmium or arsenic in the mother’s blood and the risk of the infant being small for its gestational age at birth. Women with the highest levels of mercury in their blood or arsenobetaine (an arsenic metabolite) in their urine had a small increased risk (1.6 times) of giving birth to a SGA infant compared to women with the lowest levels of these metals.

Further research is needed to confirm the observed associations between these metals and risk of SGA births. The risk of mercury and arsenobetaine exposure from fish and shellfish must be weighed against the benefits of fish consumption on fetal growth. By following fish consumption advice (, Canadians can reduce their exposure to mercury while enjoying the health benefits of eating fish.