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PEDIATRICS Vol. 110 No. 1 July 2002, pp. 110-118

Maternal Bone Lead as an Independent Risk Factor for Fetal Neurotoxicity: A Prospective Study

Ahmed Gomaa, MD, ScD^*,, Howard Hu, MD, ScD^*,, David Bellinger, PhD^||, Joel Schwartz, PhD^*,, Shirng-Wern Tsaih, ScD^*,, Teresa Gonzalez-Cossio, PhD^¶, Lourdes Schnaas^#, Karen Peterson, ScD^**, Antonio Aro, PhD^* and Mauricio Hernandez-Avila, MD, ScD^¶

^* Department of Environmental Health, Harvard School of Public Health, Boston, Massachusetts
National Institute for Occupational Safety and Health, Morgantown, West Virginia
Channing Laboratory, Department of Medicine, Brigham and Women’s Hospital, Harvard Medical School, Boston, Massachusetts
^|| Neuroepidemiology Unit, Children’s Hospital, Harvard Medical School, Boston, Massachusetts
^¶ Centro de Investigaciones en Salud Poblacional, Instituto Nacional de Salud Publica, Cuernavaca, Morelos, Mexico
^# Department of Developmental Neurobiology, Instituto Nacional de Perinatologia, Mexico City, Mexico
^** Department of Nutrition, Department of Environmental Health, Harvard School of Public Health, Boston, Massachusetts

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 µ 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.

Key Words: lead • bone • epidemiology • neurotoxins

Abbreviations: K-XRF, K-x-ray fluorescence • BSID, Bayley Scales of Infant Development • MDI, Mental Development Index • PDI, Psychomotor Development Index • SD, standard deviation

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Received for publication Aug 23, 2001; Accepted Feb 4, 2002.

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