Table 1.
Characteristics of the Children at the Age of Five Years and of Their Mothers.*
| Characteristic | Children with Complete Data (N=154) |
Children with Incomplete Data (N=21) |
Children Who Did Not Participate (N=65) |
|---|---|---|---|
| Children | |||
| Age at testing (mo) | 60.6±1.0 | 60.6±0.9 | — |
| Female sex (%) | 52.6 | 45.5 | 53.9 |
| Weeks of gestation | 39.5±1.2 | 39.8±1.0 | 39.4±1.2 |
| Birth weight (g) | 3295±405 | 3400±496 | 3304±473 |
| Transferrin saturation (%) | 22.5±9.4 | 23.5±6.6 | — |
| Blood lead concentration (µg/dl)† |
|||
| Lifetime average | 7.4±4.3 | 7.3±3.6 | — |
| Peak | 11.1±7.1 | 12.6±8.2 | — |
| Concurrent | 5.8±4.1 | 6.4±7.5 | — |
| Average in infancy | 7.0±3.8 | 7.4±3.4 | 7.2±4.1 |
| IQ‡ | 89.8±11.4 | 85.6±12.2 | — |
| Mothers | |||
| No. of prenatal visits | 11.1±4.1 | 10.2±5.0 | 10.4±3.7 |
| HOME total score§ | 27.3±7.1 | 28.7±6.1 | 27.8±6.2 |
| Yearly income >$15,000 (%) | 35.7 | 45.5 | — |
| Smoked during pregnancy (% | )20.1 | 38.1 | 27.7 |
| Age at delivery (yr) | 25.0±6.7 | 25.8±4.6 | 23.8±5.6 |
| Parity | 1.4±1.4 | 1.6±1.3 | 1.3±1.4 |
| Nonwhite race (%) | 73.4 | 68.2 | 66.2 |
| Education >12 yr (%) | 31.2 | 22.7 | — |
| IQ‡ | 81.9±12.7 | 80.5±13.6 | 83.8±10.2 |
Data obtained at the age of three years were similar to the data obtained at five years of age and are not shown. Differences among the groups were not significant (P<0.05) for any variable at the age of either three or five years. Plus– minus values are means ±SD. To convert values for lead to micromoles per liter, multiply by 0.0483.
The lifetime average blood lead concentration was estimated at the ages of 3 and 5 years by computing the area under the blood lead curve (AUC) from 6 through 36 months and from 6 through 60 months, respectively, and then dividing the AUC by its corresponding age span to yield an average on the mi-crogram-per-deciliter scale. The peak blood lead concentration was the child’s highest measured blood lead concentration through the age of three or five years. The concurrent blood lead concentration was the concentration measured on the day of cognitive testing, and the average blood lead concentration in infancy was the AUC from 6 through 24 months.
The Stanford–Binet Intelligence Scale, fourth edition (abbreviated), was used to assess IQ.
The Home Observation for Measurement of Environment Inventory (HOME) is an index that reflects the quality and quantity of emotional and cognitive stimulation in the home environment. The total score is the sum of 39 items, each scored as present (1) or absent (0), in six categories (maternal responsivi-ty, acceptance of child, organization of the home environment, provision of play materials, maternal involvement with the child, and the variety of stimulation).