Table 1.

Characteristics of Women According to the Interval Between First and Second Live, Singleton Births (n = 192,041), Western Australia, 1980–2010

Characteristic	Interpregnancy Interval												P Value
	<6 Months		6–11 Months		12–17 Months		18–23 Months		24–59 Months		≥60 Months
	No.	Row %	No.	Row %	No.	Row %	No.	Row %	No.	Row %	No	Row %
All	5,871	3	29,158	15	42,756	22	34,405	18	64,926	34	14,925	8
Age at first birth, years													<0.001
14–19	1,354	5	3,648	15	4,049	16	3,224	13	8,727	35	4,141	16
20–24	2,115	4	8,634	16	11,599	21	9,205	17	18,142	33	5,622	10
25–29	1,499	2	9,865	15	15,967	24	13,084	19	23,231	34	3,717	6
30–34	692	2	5,463	15	8,997	25	7,226	20	12,383	34	1,291	4
≥35	211	3	1,548	19	2,144	26	1,666	20	2,443	30	154	2
Race/ethnicitya													0.243
White	4,716	3	25,686	15	38,702	23	31,324	18	57,360	34	12,911	7
Nonwhite	1,155	5	3,472	16	4,054	19	3,081	14	7,566	36	2,014	9
Socioeconomic statusb													<0.001
Lowest 20%	522	4	2,050	16	2,908	23	2,170	17	3,931	31	939	8
20%–39%	538	3	2,484	16	3,524	23	2,700	17	4,946	32	1,241	8
40%–59%	1,161	4	5,078	16	7,018	22	5,660	17	10,690	33	2,820	9
60%–79%	2,132	3	10,209	15	14,817	21	12,316	18	23,959	35	5,618	8
Highest 20%	1,518	2	9,337	15	14,489	23	11,559	18	21,400	34	4,307	7
Residence													<0.001
Metropolitan	4,030	3	20,394	15	30,201	22	24,833	18	47,925	35	10,727	8
Nonmetropolitan	1,841	3	8,764	16	12,555	23	9,572	18	17,001	32	4,198	8
No. of children													<0.001
2	2,745	2	15,495	13	25,221	21	22,133	18	45,810	38	10,404	8
3	1,809	4	8,843	18	12,524	25	9,167	18	14,334	28	3,506	7
≥4	1,317	7	4,820	24	5,011	25	3,105	15	4,782	24	1,015	5

^a Race/ethnicity was defined as white or nonwhite: nonwhite included Aboriginal and Torres Strait Islander, Asian, Indian, black, Polynesian, Maori, and other races/ethnicities.

^b Socioeconomic status was defined based on the Statistical Local Area of the mother and the Socioeconomic Index for Areas (SEIFA) score for relative advantage and disadvantage produced by the Australian Bureau of Statistics (17).