Reasons for testing and exposure sources among women of childbearing age with moderate blood lead levels

Risk-Factor Based Lead Screening and Correlation with Blood Lead Levels in Pregnancy

OBJECTIVES

Lead exposure has devastating neurologic consequences for children and may begin in utero. The American College of Obstetricians and Gynecologists recommends prenatal lead screening using a risk factor-based approach rather than universal blood testing. The clinical utility of this approach has not been studied. We evaluated a risk-factor based questionnaire to detect elevated blood lead levels in pregnancy.

METHODS

We performed a secondary analysis of a cohort of parturients enrolled to evaluate the association of lead with hypertensive disorders of pregnancy. We included participants in this analysis if they had a singleton pregnancy ≥ 34 weeks' gestation with blood lead levels recorded. Participants completed a lead risk factor survey modified for pregnancy. We defined elevated blood lead as ≥ 2 μg/dL, as this was the clinically reportable level.

RESULTS

Of 102 participants enrolled in the cohort, 92 had blood lead measured as part of the study. The vast majority (78%) had 1 or more risk factor for elevated lead using the questionnaire yet none had clinical blood lead testing during routine visits. Only two participants (2.2%) had elevated blood lead levels. The questionnaire had high sensitivity but poor specificity for predicting detectable lead levels (sensitivity 100%, specificity 22%).

CONCLUSIONS FOR PRACTICE

Prenatal risk-factor based lead screening appears underutilized in practice and does not adequately discriminate between those with and without elevated blood levels. Given the complexity of the risk factor-based approach and underutilization, the benefit and cost-effectiveness of universal lead testing should be further explored.

Near-Infrared Fluorescent Probe for Sensitive Detection of Pb(II) Ions in Living Cells

A new near-infrared fluorescent probe (NIR-PbP) for sensitive detection of Pb(II) ions in solution and living cells has been rationally designed and synthesized. The NIR-PbP is inherently non-fluorescent and gains fluorescence in the presence Pb(II) ions. The ion detection is based on Pb(II)-induced unmasking the fluorophore through the opening of the spyrocycle, with more than 500-fold fluorescence for sub-micromolar Pb(II) concentration. The NIR-PbP has high sensitivity, good photo-stability, low detection limit, and reversible response to Pb(II) ions.

Detrimental effects of maternal lead exposure during pregnancy and lactation on molar development in the young rat

The purpose of this animal study was to investigate the influence of maternal lead exposure during pregnancy and lactation on molar development in the offspring. Scanning electron microscopy revealed no significant differences in the molar morphology among the groups. However, in all the experimental groups, deep, wide cracks were found in the occlusal enamel. Further, the experimental groups had smaller molar diameters than the control group, lead exposure during lactation had a greater influence on the molar size in the offspring, and the groups with the higher dose of lead exposure during pregnancy and lactation had significantly smaller molar sizes than the groups that received the lower dose. The mesiodistal and buccolingual diameters of molars were measured as 3.10 ± 0.07 and 1.95 ± 0.04 mm for control group, 2.97 ± 0.08 and 1.94 ± 0.01 mm for lactation group of low dose, 2.96 ± 0.05 and 1.84 ± 0.02 mm for lactation group of high dose, 3.09 ± 0.06 and 1.94 ± 0.04 mm for pregnancy group of low dose, and 3.02 ± 0.06 and 1.85 ± 0.06 mm for pregnancy group of high dose, respectively.

Exposure sources and reasons for testing among women with low blood lead levels

Previous research has focused on highly elevated blood lead (PbB). This study examined reasons for testing and potential sources of exposure among women with PbBs less than 0.72 μmol/l (15 μg/dl). A questionnaire was mailed to 18- to 49-year-old women in upstate New York, USA, who were PbB tested in 2007. The most common testing reason was pregnancy among 125 women who returned the questionnaire. Among women tested for PbB during pregnancy, doctors ordered approximately 80% of tests regardless of lead level. Few women with PbBs less than 0.24 μmol/l (5 μg/dl) reported a potential source of lead exposure. However, among women with PbBs of 0.24-0.71 μmol/L (5-14.9 μg/dl), 29.2% had a job and 21.2% had a hobby with potential lead exposure. There are systematic differences in reasons for testing and exposure sources among women with PbBs less than 0.72 μmol/l and these differences have implications for screening.

The placenta as a barrier for toxic and essential elements in paired maternal and cord blood samples of South African delivering women

Environmental toxicants such as metals may be detrimental to foetus and infant development and health because of their physiological immaturity, opportunistic and differential exposures, and a longer lifetime over which disease, initiated during pregnancy and in early life, can develop. The placental mechanisms responsible for regulation of absorption and excretion of elements during pregnancy are not fully understood. The aim of this paper is to assess the correlation for selected toxic and essential elements in paired whole blood samples of delivering women and cord blood, as well as to evaluate the placental permeability for selected elements. Regression analyses used to assess this correlation in 62-paired samples of maternal and cord whole blood of delivering women show that the concentrations of mercury, lead, cobalt, arsenic and selenium in maternal and cord blood differed statistically. Lead, cobalt, arsenic and selenium appear to pass the placental barrier by a diffusion mechanism. It was also found that the mercury levels in cord blood were almost double those of the mother, suggesting that the foetus may act as a filter for the maternal mercury levels during pregnancy. Transplacental transfer for arsenic and cobalt was 80% and 45%, respectively, suggesting that the placenta modulates the rate of transfer for these elements. Cadmium, manganese, copper and zinc levels did not show statistically significant correlations between two compartments (maternal versus cord whole blood). The study confirms that most of the toxic metals measured have an ability to cross the placental barrier.

Elevated blood lead levels in pregnant women: identification of a high-risk population and interventions

There has been a significant decrease in the number of preschool children with elevated blood lead levels (BLL), from 88.2 to 4.4 per 10,000 children over the last three decades as shown by National Health and Nutritional Examination Survey (NHANES) data. However, there are still certain high-risk populations that have not been well studied. One such group is that of pregnant women. During pregnancy, BLL tends to increase due to greater bone turnover, which causes release of lead stored in bone. This increase may not affect the pregnant woman's health directly but could be extremely harmful to the rapidly developing central nervous system in the fetus as it crosses the placenta easily. This current study was undertaken to estimate the prevalence of elevated BLL in pregnant women in a community hospital, monitor the effect of routine preventive practices on maternal BLL, and to elucidate the relationship between maternal and neonatal BLL and their anthropometric indices. A retrospective chart review was conducted on all hospital deliveries occurring in the first six years after the initiation of universal blood lead screening of pregnant women (n=6880). The prevalence of elevated lead (> or =10 microg/dL) in our patient population was 1.7%. The factors associated with elevated lead levels were recent immigration to the US, poor socioeconomic status and low educational levels. Simple interventions such as hand washing as well as calcium and iron supplementation significantly reduced maternal BLL from 16.82+/-9.5 to 11.48+/-9.3 microg/dL (P<0.0001). A significant correlation (r=0.4, P<0.007) is present between the post-intervention but not the pre-intervention maternal BLL and the neonatal BLL. Given the vulnerability of the developing fetal brain and that CNS complications are associated with elevated lead levels, antenatal lead screening should be part of routine prenatal care. Simple preventive measures may play a role in decreasing maternal BLL and thereby decreasing transplacental transfer of lead to the fetus.

Lead and immune function

The heavy metal lead is a widely deposited environmental toxicant known to impact numerous physiological systems, including the reproductive, neurological, hepatic, renal, and immune systems. Studies illustrating the capacity of lead to impair immune function and/or host resistance to disease date back to at least the 1960s. However, it has only been in recent years that lead has been recognized among a new category of immunotoxicants-those that dramatically shift immune functional capacity while producing only modest changes to immune cell populations and lymphoid organs. These relatively noncytotoxic immunomodulating chemicals and drugs represent the immunotoxic hazards most difficult to identify and problematic for risk assessment using historic approaches. As a result, such environmental factors are also among the most likely to contribute to chronic immune-related disease at relevant exposure levels. This review considers the animal and human evidence that lead exposure can produce a stark shift in immune functional capacity with a skewing predicted to elevate the risk of atopic and certain autoimmune diseases. At the same time, host defenses against infectious agents and cancer may be reduced. Age-based exposure studies also suggest that levels of blood lead previously thought to be safe, that is, below 10 microg/dl, may be associated with later life immune alterations.

Teratogen update: lead and pregnancy

This review focuses on the impacts of lead exposure on reproductive health and outcomes. High levels of paternal lead exposure (>40 microg/dl or >25 microg/dl for a period of years) appear to reduce fertility and to increase the risks of spontaneous abortion and reduced fetal growth (preterm delivery, low birth weight). Maternal blood lead levels of approximately 10 microg/dl have been linked to increased risks of pregnancy hypertension, spontaneous abortion, and reduced offspring neurobehavioral development. Somewhat higher maternal lead levels have been linked to reduced fetal growth. Some studies suggest a link between increased parental lead exposure and congenital malformations, although considerable uncertainty remains regarding the specific malformations and the dose-response relationships. Common methodological weaknesses of studies include potential exposure misclassifications due to the frequent unavailability of exposure biomarker measurements at biologically appropriate times and uncertainty regarding the best exposure biomarker(s) for the various outcomes. A special concern with regard to the pregnant woman is the possibility that a fetus might be exposed to lead mobilized from bone stores as a result of pregnancy-related metabolic changes, making fetal lead exposure the result of exposure to exogenous lead during pregnancy and exposure to endogenous lead accumulated by the woman prior to pregnancy. By reducing bone resorption, increased calcium intake during the second half of pregnancy might reduce the mobilization of lead from bone compartments, even at low blood lead levels. Subgroups of women who incurred substantial exposures to lead prior to pregnancy should be considered to be at increased risk.

Lead poisoning in pregnancy: a case study with implications for midwives

Lead poisoning remains a significant problem in the United States affecting the health of women and children. Although the damage is greatest at higher levels of accumulation, no level of lead has been found to be safe. Over the last 25 years, the blood level of lead thought to be associated with toxicity has dropped dramatically, from to 60 mcg/dL in 1960 to 10 mcg/dL today. Studies confirm that exposure to lead causes kidney damage, encephalopathy, and impaired cognitive function in children and in adults. Recent evidence indicates children with levels less than 10 mcg/dL may suffer from compromised development and intellectual performance later in life. This article discusses the case of a woman found to have lead poisoning during pregnancy. Environmental sources of lead, implications for the immediate and future health of the fetus and mother, and techniques clinicians can use in their practice to minimize the adverse effect of lead on their clients are reviewed.

Lead poisoning among pregnant women in New York City: risk factors and screening practices

This article presents information on pregnant women with incident blood lead levels (BLLs) of 20 microg per deciliter or greater as reported to the New York City Department of Health between September 1996 and June 1999 (n = 33). Almost half of the women were diagnosed during their third trimester of pregnancy, often at their first prenatal visit. The median BLLs at incidence and at last report among women who were retested were 25 and 15 gamma/dL, respectively, a 40% decline. The median incident BLL among newborns (n = 25) was 12 microg/dL. The BLLs were inversely associated with maternal age and length of time in the United States and directly associated with gestational age and pica behavior. Cases were more than twice as likely to be foreign-born women than all women who gave birth in New York City. Prenatal care facilities employing a policy of universal blood lead testing of all pregnant women at the time of their first visit reported disproportionate numbers of cases, accounting for 77% of cases yet only 11% of all births citywide. The findings suggest that (1) the promulgation of recent rules and guidelines for lead risk assessment and screening among pregnant women appears to have been effective in identifying cases that might not have otherwise come to light; (2) case management and environmental interventions were initiated promptly; (3) cases experienced, on average, significant BLL reductions over time; and (4) there is a need for additional public health interventions for pregnant women in urban, multicultural centers. While the data suggest that universal screening may increase case finding among high-risk, immigrant populations, further studies and surveillance are needed to determine systematically the most effective approach.