Table 2.

Incidence rate of breast cancer in women who had first delivery in 2007.

	No. of patients(N = 235,872)	No. of Events(N = 2,971)	Incidence rate per 10,000 person years (95% CI)	10-Year cumulative rate	P-value by log rank test	Crude HR(95% CI)	P-value
Age at first delivery					<.0001
<30	115507	849	5.92 (5.53-6.33)	0.39 (0.35-0.42)		Ref
30-39	116381	2021	14.00 (13.40-14.62)	1.01 (0.95-1.07)		2.36 (2.18, 2.56)	<.0001
40-49	3984	101	20.56 (16.92-24.99)	2.09 (1.65-2.54)		3.47 (2.82, 4.26)	<.0001
Age at last delivery					<.0001
20-29	66222	439	5.34 (4.86-5.86)	0.38 (0.34-0.43)		Ref
30-39	163948	2396	11.77 (11.31-12.25)	0.82 (0.78-0.87)		2.20 (1.99, 2.44)	<.0001
40-49	5702	136	19.32 (16.33-22.86)	1.85 (1.50-2.20)		3.62 (2.99, 4.39)	<.0001
Number of delivery					<.0001
1	105091	1681	12.92 (12.32-13.56)	1.00 (0.94-1.06)		Ref
2	118202	1194	8.12 (7.67-8.60)	0.52 (0.48-0.56)		0.63 (0.58, 0.68)	<.0001
>=3	12579	96	6.12 (5.01-7.47)	0.39 (0.28-0.50)		0.47 (0.38, 0.58)	<.0001
Interval of delivery (women with two deliveries)					0.0973
≥ 10 months, < 12 months	570	9	12.70 (6.61-24.42)	0.70 (0.02-1.39)		2.48 (1.18, 5.22)	0.0170
≥ 12 months, < 24 months	29231	295	8.12 (7.25-9.11)	0.58 (0.49-0.67)		1.59 (1.09, 2.31)	0.0159
≥ 24 months, < 36 months	41757	421	8.12 (7.38-8.93)	0.50 (0.44-0.57)		1.59 (1.10, 2.30)	0.0144
≥ 36 months, < 48months	26936	273	8.15 (7.23-9.17)	0.50 (0.42-0.59)		1.59 (1.09, 2.32)	0.0159
≥ 48 months, < 60 months	15187	166	8.78 (7.54-10.22)	0.51 (0.40-0.63)		1.71 (1.16, 2.53)	0.0066
≥ 60 months	4521	30	5.25 (3.67-7.51)	0.38 (0.20-0.55)		Ref