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Maternal bone lead as an independent risk factor for fetal neurotoxicity: a prospective study
Ahmed Gomaa1, Howard Hu, David Bellinger
1Department of Environmental Health, Harvard School of Public Health, Boston, Massachusetts, USA.
Insights
Maternal bone lead levels, particularly in trabecular bone, are a significant predictor of impaired infant mental development. This finding highlights a public health concern due to lead
Area of Science:
- Environmental Health
- Neurodevelopmental Pediatrics
- Toxicology
Background:
- Lead exposure in utero is a known risk factor for adverse infant neurodevelopment.
- Previous studies on umbilical cord blood lead levels have shown inconsistent associations with infant mental development.
- Maternal bone lead, a reservoir for lead, may offer a more accurate measure of cumulative fetal exposure.
Purpose of the Study:
- To compare the predictive power of umbilical cord blood lead and maternal bone lead levels for infant mental development.
- To investigate lead levels in maternal cortical and trabecular bone as predictors of neurodevelopmental outcomes.
- To assess the independent contribution of maternal bone lead to impaired infant mental development in a prospective study.
Main Methods:
- Prospective study involving 197 mother-infant pairs in Mexico City.
- Measurement of umbilical cord blood lead using graphite furnace atomic absorption spectroscopy.
- Quantification of maternal tibial (cortical) and patellar (trabecular) bone lead using K-x-ray fluorescence.
- Assessment of infant mental development at 24 months using the Bayley Scales of Infant Development-II.
Main Results:
- Higher maternal trabecular bone lead levels were independently and inversely associated with infant Mental Development Index (MDI) scores.
- Increased trabecular bone lead was linked to significant decrements in adjusted MDI scores (e.g., 5.4-7.2 points).
- A 2-fold increase in cord blood lead was associated with a 3.1-point MDI decrement, comparable to prior findings.
Conclusions:
- Maternal trabecular bone lead is an independent risk factor for impaired infant mental development at 24 months.
- Mobilization of maternal bone lead stores likely contributes to fetal neurodevelopmental deficits.
- The long-term retention of lead in bone presents a significant public health challenge for infant neurodevelopment.
Objective:
A number of prospective studies have examined lead levels in umbilical cord blood at birth as predictors of infant mental development. Although several have found significant inverse associations, others have not. Measurement of lead levels in maternal bone, now recognized as the source of much fetal exposure, has the potential to serve as a better or complementary predictor of lead's effect on the fetus. Our objective was to compare lead levels in umbilical cord blood and maternal bone as independent predictors of infant mental development using a prospective design.
Methods:
We recruited women who were giving birth at 3 maternity hospitals in Mexico City that serve a homogeneous middle-class community. Umbilical cord blood lead levels were measured by graphite furnace atomic absorption spectroscopy, and maternal lead levels in cortical (tibial) and trabecular (patellar) bone were measured within 4 weeks of giving birth using a 109-Cd K-x-ray fluorescence instrument. At 24 months of age, each infant was assessed using the Bayley Scales of Infant Development-II (Spanish Version).
Results:
A total of 197 mother-infant pairs completed this portion of the study and had data on all variables of interest. After adjustment for other well-known determinants of infant neurodevelopment, including maternal age, IQ, and education; paternal education; marital status; breastfeeding duration; infant gender; and infant illness, lead levels in umbilical cord blood and trabecular bone were significantly, independently, and inversely associated with the Mental Development Index (MDI) scores of the Bayley Scale. In relation to the lowest quartile of trabecular bone lead, the second, third, and fourth quartiles were associated with 5.4-, 7.2-, and 6.5-point decrements in adjusted MDI scores. A 2-fold increase in cord blood lead level (eg, from 5 to 10 micro g/dL) was associated with a 3.1-point decrement in MDI score, which is comparable to the magnitude of effect seen in previous studies.
Conclusion:
Higher maternal trabecular bone lead levels constitute an independent risk factor for impaired mental development in infants at 24 months of age. This effect is probably attributable to mobilization of maternal bone lead stores, a phenomenon that may constitute a significant public health problem in view of the long residence time of lead in bone.