Table 3.

Concurrent blood lead concentration and mean IQ scores by characteristics of children and their mothers (n = 1,333).

Covariate	No.	Median concurrent blood lead (μg/dL) (5th–95th percentiles)	IQ ± SD
Child
Female	669	9.0 (2.4–31.4)	93.8 ± 18.3
Male	664	9.9 (2.6–35.7)	92.5 ± 20.0
Birth weight (g)
< 3,000	359	10.0 (2.2–28.7)	88.6 ± 18.0
3,000 to < 3,500	519	9.9 (2.4–34.2)	93.6 ± 19.3
≥3,500	455	9.1 (2.8–34.7)	96.3 ± 19.3
Gestation at delivery (weeks)
< 38	144	8.9 (3.1–37.9)	83.5 ± 18.6
38 to < 42	1,071	9.8 (2.5–33.2)	94.1 ± 18.6
≥42	115	10.0 (3.2–24.8)	96.3 ± 22.1
Birth order
1	479	9.0 (2.1–32.6)	96.7 ± 18.9
2	407	10.0 (2.6–31.4)	93.6 ± 19.2
≥3	446	10.0 (3.0–36.9)	89.0 ± 18.7
Maternal
Race (only U.S. cohorts)
White	278	7.9 (1.3–22.0)	100.6 ± 20.1
Nonwhite	401	7.1 (2.8–21.5)	84.9 ± 12.8
Age at delivery (years)
< 25	650	10.5 (3.0–32.0)	89.6 ± 17.2
≥25	683	9.0 (2.1–34.7)	96.5 ± 20.3
Maternal IQ
< 85	618	10.0 (2.9–32.0)	83.3 ± 15.0
≥85	715	9.0 (2.1–34.3)	101.6 ± 18.3
Education at delivery (grade)
< 12	710	12.0 (4.1–35.5)	90.4 ± 18.8
12	397	8.7 (2.4–34.3)	91.1 ± 17.7
≥12	226	5.5 (1.1–15.2)	105.5 ± 18.0
HOME score
< 30	276	9.4 (3.0–43.0)	77.9 ± 14.9
30 to < 40	561	10.0 (2.8–32.2)	88.3 ± 15.4
≥40	496	9.5 (2.0–22.0)	107.0 ± 15.8
Married
Yes	896	10.0 (2.7–37.5)	96.2 ± 20.5
No	436	8.1 (2.4–22.0)	87.0 ± 14.3
Prenatal smoking
Yes	453	11.5 (3.2–33.2)	89.5 ± 17.2
No	876	8.7 (2.2–33.6)	94.9 ± 19.9
Prenatal alcohol ingestion
Yes	278	10.1 (2.2–25.0)	99.3 ± 19.4
No	1,035	9.5 (2.7–34.3)	91.7 ± 18.8