Maternal Bone Lead Levels Pose Toxic Prenatal Risk
For immediate release: July 01, 2002
Boston, MA- In the first study to assess how stores of lead in the bones of pregnant women might be associated with the later brain development of their infants, researchers from the Harvard School of Public Health and Harvard Medical School have concluded that elevated maternal bone lead levels are linked to impaired cognitive development in infants. The researchers also found that maternal bone lead serves as a distinct marker of prenatal lead exposure-and consequent health risk-- independent of umbilical cord blood lead levels or postnatal circulating blood lead levels.
Given the lengthy amount of time lead can reside in maternal bone and that bone is demineralized into the blood during pregnancy, the findings highlight a potentially significant public health problem, linking the history of a mother's lead exposure to risk for the next generation. The study appears in the July issue of the journal Pediatrics.
Although much attention has been paid to public health efforts to reduce lead exposure in children between the ages of six months and five years, when environmental lead exposures (such as from leaded paint in old houses) tend to be greatest, less attention has been paid to understanding the transfer of lead from mother to fetus and its resulting health effects.
In this study, participants included 197 mother-infant pairs from three maternity hospitals in Mexico City. Umbilical cord and maternal blood lead levels were measured within 12 hours of delivery, and maternal tibial and patellar bone lead levels were measured within four weeks of having given birth. At 12 and 24 months the blood lead levels of the mother-infant pairs were measured again and infant mental development was assessed using the Bayley Scales of Infant Development-II (BSID-II Spanish Version) and scored using the Mental Development Index (MDI) and Psychomotor Development Index (PDI).
Umbilical cord blood lead levels among the infants in the study averaged 6.7 micrograms per deciliter and ranged from 1.2 to 21.6. The lead levels in the maternal patella and tibia bones averaged 17.9 and 11.5 respectively. The blood lead levels in the infants rose with age, with average blood lead levels of 7.2 micrograms per deciliter at 12 months and 8.4 at 24 months. The Centers for Disease Control and Prevention has set a "level of concern" at 10 micrograms per deciliter. Even at low levels, lead poisoning in children can cause IQ deficiencies, reading and learning disabilities, impaired hearing, reduced attention spans, hyperactivity and other behavior problems.
The researchers found that infants who had higher cord blood lead levels and whose mothers had higher patella bone lead levels had lower MDI scores. When maternal patella bone lead levels were divided into four groups, with the lowest serving as the reference point, the three higher infant groups all had lower MDI scores. Higher tibia lead levels were associated with lower MDI scores but not as significantly as lead levels in the patella.
Lower MDI scores were directly attributed to increased levels of lead in maternal bone when researchers factored out cord lead levels, postnatal blood lead levels and other variables. Additionally, prenatal lead exposure was found to affect cognitive development scores (MDI) more than motor-skill development scores (PDI).
"The study shows that the consequences of maternal lead exposure on fetal neurodevelopment are worse than previously thought," said Howard Hu, principal investigator of the study and associate professor of occupational medicine in the Department of Environmental Health at the Harvard School of Public Health. "The consequences must be thought of not only in terms of any lead exposure that a woman might endure during pregnancy, but lead exposure a woman might have endured over the years prior to the pregnancy with accumulation in her bones, and subsequent release during pregnancy."
Regarding ways pregnant women can reduce the risk of passing lead to their unborn child, Hu added, "Some studies suggest that calcium supplementation during pregnancy can decrease the mobilization of lead from maternal bone, pediatricians and obstetricians might consider recommending such an option to women with a history of lead exposure who are planning to become pregnant."
The study was supported by grants from the March of Dimes, National Institute of Environmental Health and Safety, US and Consejo National de Cienca y Technologia and CONSERVA, Department of Federal District, Mexico.
For further information, please contact:
Office of Communications
Harvard School of Public Health
677 Huntington Avenue
Boston, MA 02115