Abstract
Lead levels were measured by inductively coupled plasma mass spectrometry (ICP-MS) in umbilical cord blood samples of 150 neonates in an urban inner-city hospital. The mean (SD) gestation and birth weight of our cohort were 38.8 (1.7) weeks and 3,217 (519) grams. There were 89% African-Americans, 53% males and 79% were born via vaginal delivery. Mean (SD) maternal age was 24.5 (5.8) years. History of drug abuse and smoking was reported in 8.7% and 10.7% respectively, with only 1 mother reporting a history of high lead level in childhood. Prenatal vitamin intake was reported in 99.3%. Cord blood lead level was available in 144 patients, with lead level of <1μg/dL seen in 141 (97.9%) and>1 in 3 (2.1%) patients. No patient had cord blood lead level of >2μg/dL. High lead levels during childhood in high-risk urban population, however, suggest the need for intensive efforts for prevention of environmental exposure to lead in early childhood.
Keywords
Introduction
High lead level in the body has been known to be neurotoxic for many decades [1]. Exposure to lead during intrauterine life has been associated with fetal death, low birth weight, prematurity, altered auditory recognition memory and delay in cognitive development [2–5]. The umbilical cord blood lead levels may indicate the degree of exposure of fetus to lead. Lead in the maternal blood readily crosses the placenta and levels in cord blood and to some extent in breast milk have been noted to correlate with maternal lead level [6, 7]. Indeed, at a time of rapid brain growth during the fetal and neonatal period, any blood lead value may be toxic [8]. In women of reproductive age group, 45 to 70% of lead in the blood originates from long-term tissue stores, such as bones [9]. Lead in the bone may become bioavailable when bone tissue undergoes mineralization and resorption during pregnancy and lactation, leading to an increase in the blood lead level by 15–20% [10, 11].
The blood lead level in women of reproductive age has been shown to be inversely associated with education level, hematocrit, age, intake of thiamine, calcium and positively associated with African American or Hispanic ethnicity, high body mass index, living in urban areas, alcohol consumption and cigarette smoking [3, 12]. Schell and colleagues performed a longitudinal study of mother-infant pairs (n = 211) in Albany, NY, with maternal lead level in 2nd trimester, infant lead levels at 6 and 12 months of age and growth monitoring of infants. They noted that infants of mothers with the 2nd trimester lead level ≥3μg/dL had negative associations between blood lead and infants’ head circumference at 6 and 12 months of age; and with weight-for-age, weight-for length and upper arm circumference at 6 months of age, but this association was not seen at median maternal lead level <3μg/dL [13].
The aim of this study was to determine the prevalence of high lead level in the cord blood in a predominantly African American and publicly insured population of women delivering at Hutzel Women’s Hospital, Detroit, Michigan.
Patients and methods
This was a hospital based prospective observational study, conducted from May 2012 through July 2012 at Hutzel Women’s Hospital, Detroit. All births were eligible for the study in that period, with the exclusion of multiple births and neonates with major congenital anomalies. The study was approved by the Institutional Review Board, Wayne State University. We collected data on factors thought to affect the lead level including race, maternal smoking, illicit drugs, and prior history of high lead level in mother, history of pica and postal zip code and year of construction of residence. Data collection was by chart review and a brief questionnaire administered to mothers after delivery. Cord blood samples were collected in lead-free EDTA tubes. The specimens were stored in a refrigerator in the Labor and Delivery unit and were sent every two days to the laboratory for analysis. Blood samples were analyzed using inductively coupled plasma mass spectrometry. Whole blood was brought to room temperature and mixed thoroughly on a rocker at room temperature for 30 minutes. Whole blood (50 microliters) was digested in 2.5 mL of 0.019% Tetramethyl Ammonium Hydroxide and vortex mixed to ensure complete digestion of whole blood. The digested whole blood was aspirated in to ICP-MS (Nexion 500X, Perkin-Elmer, USA) for lead analysis.
Results
A total of 150 patients were enrolled for the study, of whom we were able to analyze the cord blood level in 144 patients. The mean (SD) gestational age and birth weight were 38.8 (1.7) weeks and 3,217 (519) grams, with 7 neonates born prematurely (<37 weeks gestation). The majority (89%) of the participants was African-American, 53% were males and 79% were born via vaginal delivery. Mean (SD) maternal age was 24.5 (5.8) years. History of drug abuse and smoking was obtained in 8.7% and 10.7% respectively, with only 1 mother reporting a history of high lead level in childhood (Table 1). Prenatal vitamin intake was reported in 99.3%. Cord blood lead level <1μg/dL was noted in 141 (97.9%) and >1μg/dL in 3 (2.1%) patients. No patient had cord blood lead level of >2μg/dL. We further compared this prevalence to the prevalence of high lead level during childhood in our patient population. At our University laboratory, among 16,000 samples analyzed for general screening in the year 2009 for children less than 8 years of age, 6% had lead level ≥5μg/dL and 2% had lead level ≥10μg/dL.
Discussion
While aggressive prevention efforts by Michigan Department of Community Health have helped to reduce harmful exposure to lead in children, a significant problem still exists. Michigan still ranks fifth worst in the United States in this area. Only 21% of Michigan children under 6 years of age undergo testing for lead annually. More than half of the school-aged children in the Detroit Public School system have had harmful exposures to lead at some point [14].
Despite this high prevalence of lead exposure during early childhood, we noted that cord blood lead levels were below 1μg/dL in the vast majority of our patients. These data suggest that lead exposure starts in this inner-city population in the postnatal period, with lowering of blood lead levels by child bearing age in women. Previous studies have noted higher cord blood lead level in premature births, and in neonates of women who smoked before and during pregnancy [6]. In our study, most neonates were born at term gestation and the rate of smoking was relatively low.
Center for Disease Control does not recommend routine blood lead testing of all pregnant women in the United States; however, assessment for lead exposure by risk factor questionnaire or blood lead testing is recommended early in pregnancy [15]. State and/or local health departments should identify risk factors specific to the community to provide guidance to health care providers [15].
A recent study by Hanna-Attisha and colleagues, noted a significant increase in blood lead levels in children associated with a change in the water supply source in Flint, MI [16]. This study is thought-provoking and serves as a strong reminder for clinicians to remain vigilant for safe-drinking water challenges in our communities. In these situations, as suggested by CDC, risk assessment and blood lead level testing early in pregnancy [15], at birth (cord blood) and during early childhood would be prudent to reduce the potential harm associated with lead exposure to developing fetus.
Conclusion
In a contemporary cohort of high risk, predominantly African-American neonates, delivered in an inner city urban hospital, there was no evidence of fetal exposure to lead at the time of delivery, with majority below 1μg/dL. High lead levels during childhood suggest the need for intensive efforts for prevention of environmental exposure to lead in early childhood and to remain vigilant for any future challenges, including safety of drinking water.