TABLE 1.

Characteristics of women and their offspring in the Collaborative Perinatal Project, 1959–1974

	Full sample* (n = 52,919)		Sibling sample† (n = 16,619)
	Mean (SD‡) or no.	%	Mean (SD) or no.	%
Maternal smoking during pregnancy§
0	25,315	47.8	7,730	46.5
1–9	9,398	17.8	2,814	16.9
10–19	6,403	12.1	2,069	12.5
≥20	11,803	22.3	4,006	24.1
Mean maternal age (years)	24.2 (6.0)		24.0 (5.5)
Race/ethnicity¶
White	24,177	45.9	8,317	50.2
Black	24,549	46.6	7,572	45.7
Other	3,978	7.6	675	4.1
Offspring sex
Male	26,842	50.7	8,403	50.6
Female	26,077	49.3	8,216	49.4
Mean family socioeconomic status percentile#	46.9 (21.6)		47.2 (21.0)
No. of siblings enrolled per family
1	36,300	68.6	—**
2	11,840	22.4	11,840	71.2
3	3,717	7.0	3,717	22.4
4	884	1.7	884	5.3
5	160	0.3	160	1.0
6	18	0.0	18	0.1

^*Collaborative Perinatal Project singleton pregnancies resulting in livebirths, with complete data on maternal smoking during pregnancy and offspring sex.

^†Collaborative Perinatal Project offspring with one or more siblings enrolled in the study.

^‡SD, standard deviation.

^§Maximum number of cigarettes smoked per day during pregnancy.

^¶Numbers of participants with missing data: full sample, n = 215; sibling sample, n = 55.

^#Numbers of participants with missing data: full sample, n = 1,493; sibling sample, n = 543.

^**Not applicable.