Abstract
This cross-sectional study was conducted to assess the association between exposure to heavy metals (lead, cadmium and mercury) during pregnancy and birth outcomes in 1578 women aged 16–50 years who delivered in Al-Kharj hospital, Saudi Arabia, in 2005 and 2006. The levels of lead, cadmium and mercury were measured in umbilical cord blood, maternal blood and the placenta. Outcome variables were anthropometric measures taken at birth, along with the risk of being small-for-gestational age (SGA). We selected the 10th percentile as the cutoff for dichotomizing measures of birth outcome. Cadmium, despite its partial passage through the placenta had the most prominent effect on several measures of birth outcome. After adjustment for potential confounders, logistic regression models revealed that crown-heel length (p=0.034), the Apgar 5-minute score (p=0.004), birth weight (p=0.015) and SGA (p=0.049) were influenced by cadmium in the umbilical cord blood. Significant decreases in crown-heel length (p=0.007) and placental thickness (p=0.022) were seen with higher levels of cadmium in maternal blood. As placental cadmium increased, cord length increased (p=0.012) and placental thickness decreased (p=0.032). Only lead levels in maternal blood influenced placental thickness (p=0.011). Mercury in both umbilical cord and maternal blood was marginally associated with placental thickness and placental weight, respectively. Conversely, placental mercury levels significantly influenced head circumference (p=0.017), the Apgar 5-minute score (p=0.01) and cord length (p=0.026). The predictions of these models were further assessed with the area under the curve (AUC) of the receiver operating curves (ROCs), which were modest (larger than 0.5 and smaller than 0.7). The independence of gestational age or preterm births on the observed effect of metals on some measures of birth outcome, suggested detrimental effects of exposure on fetal development. The magnitude of the estimated effects might not necessarily be of clinical significance for infants but may have a considerable public-health relevance given the high prevalence of exposure to heavy metals. Further research should be conducted to confirm these findings and to evaluate their long-term risks, if any.