Environmental risk factors differ between rheumatoid arthritis with and without auto-antibodies against cyclic citrullinated peptides

Table 2 Reproductive factors in women and risk of rheumatoid arthritis, Denmark 1998 to 2003

	Number of patients/controls	OR^a (95% CI)
Age at menarche
≤12 years	85/145	1 (ref)
13 years	84/130	1.08 (0.73 to 1.61)
14 years	88/105	1.39 (0.93 to 2.08)
≥15 years	94/80	1.87 (1.23 to 2.85)
Trend test (p)		0.002
Number of live-born children
0	67/86	1 (ref)
1	81/85	1.10 (0.67 to 1.79)
2	133/196	0.76 (0.48 to 1.21)
3	63/84	0.81 (0.48 to 1.37)
≥4	21/27	0.73 (0.36 to 1.51)
Trend test (p)		0.15
Spontaneous abortion
Never	237/292	1 (ref)
Ever	78/120	0.83 (0.59 to 1.18)
Test for homogeneity (p)		0.29
Breastfeeding ^b
Never	19/18	1 (ref)
Ever	279/374	0.70 (0.35 to 1.39)
Test for homogeneity (p)		0.30
Age at menopause ^c
<50 years	37/34	1 (ref)
≥50 years	47/49	0.87 (0.46 to 1.65)
Test for homogeneity (p)		0.68
Oral contraceptive pills
Never	116/165	1 (ref)
Ever	249/312	1.24 (0.91 to 1.71)
Test for homogeneity (p)		0.18
Hormone replacement therapy ^d
Never	328/436	1 (ref)
Ever	36/37	1.08 (0.63 to 1.86)
Test for homogeneity (p)		0.78

Due to missing values for some individuals, numbers do not always add up to 366 patients and 478 controls. ^aAdjusted for birth year and year or pseudo-year of RA diagnosis. ^bAmong women with at least one child. ^cAmong postmenopausal women without histories of hormone replacement therapy or surgical removal of the uterus or ovaries. ^dAmong women age 45 years or older. CI, confidence interval; OR, odds ratio; ref, reference.

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