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 ($\mathrm{\mu }\mathrm{g}/\text{dL}$) (5th–95th percentiles)	$\text{IQ}\pm \text{SD}$
Child
Female	669	9.0 (2.4–31.4)	$94.2\pm 18.6$
Male	664	9.9 (2.6–35.7)	$92.7\pm 20.4$
Birth weight (g)
$<3,000$	359	10.0 (2.2–28.7)	$88.8\pm 18.3$
3,000 to $<3,500$	519	9.9 (2.4–34.2)	$93.9\pm 19.8$
$\ge 3,500$	455	9.1 (2.8–34.7)	$96.6\pm 19.7$
Gestation at delivery (weeks)
$<38$	144	8.9 (3.1–37.9)	$84.0\pm 19.4$
38 to $<42$	1,071	9.8 (2.5–33.2)	$94.3\pm 18.9$
$\ge 42$	115	10.0 (3.2–24.8)	$97.1\pm 22.9$
Birth order
1	479	9.0 (2.1–32.6)	$97.2\pm 19.6$
2	407	10.0 (2.6–31.4)	$93.9\pm 19.7$
$\ge 3$	446	10.0 (3.0–36.9)	$89.0\pm 18.7$
Maternal
Race (only U.S. cohorts)
White	278	7.9 (1.3–22.0)	$101.9\pm 21.3$
Nonwhite	401	7.1 (2.8–21.5)	$84.9\pm 12.8$
Age at delivery (years)
$<25$	650	10.5 (3.0–32.0)	$89.6\pm 17.3$
$\ge 25$	683	9.0 (2.1–34.7)	$97.1\pm 20.9$
Maternal IQ
$<85$	618	10.0 (2.9–32.0)	$83.3\pm 15.0$
$\ge 85$	715	9.0 (2.1–34.3)	$102.2\pm 18.9$
Education at delivery (grade)
$<12$	710	12.0 (4.1–35.5)	$90.4\pm 18.8$
12	397	8.7 (2.4–34.3)	$91.1\pm 17.8$
$\ge 12$	226	5.5 (1.1–15.2)	$107.1\pm 19.4$
HOME score
$<30$	276	9.4 (3.0–43.0)	$77.9\pm 14.9$
30 to $<40$	561	10.0 (2.8–32.2)	$88.4\pm 15.4$
$\ge 40$	496	9.5 (2.0–22.0)	$107.8\pm 16.5$
Married
Yes	896	10.0 (2.7–37.5)	$96.6\pm 21.0$
No	436	8.1 (2.4–22.0)	$87.0\pm 14.4$
Prenatal smoking
Yes	453	11.5 (3.2–33.2)	$89.7\pm 17.3$
No	876	8.7 (2.2–33.6)	$95.3\pm 20.4$
Prenatal alcohol ingestion
Yes	278	10.1 (2.2–25.0)	$100.1\pm 20.2$
No	1,035	9.5 (2.7–34.3)	$91.8\pm 19.1$