Table 2.

Summary of the significant results from the studies described.

	RR, OR or SIR (95% CI)	Authors, journal, year [ref. no.]
Maternal smoking in pregnancy (≥10 cigarettes/day)	Effect seen in girls only: OR 2·57 (1·13–5·89)	Jaakkola & Gissler, Int J Epidemiol 2005 [33]
Preterm birth (gestational age <258–266 days)	OR 0·6 (0·7–1·0)	Carlens et al., Ann Rheum Dis 2009 [38]
	RR 1·1 (0·8–1·5)	Simard et al., J Rheumatol 2010 [40]
High birth weight (≥4000–4540 g)	RR 2·1 (1·4–3·3)	Mandl et al., Ann Rheum Dis 2009 [36]
	OR 3·3 (1·4–7·4)	Jacobsson et al., BMJ 2003 [37]
	OR 1·2 (0·6–2·4)	Carlens et al., Ann Rheum Dis 2009 [38]
Low birth weight (<3000 g)	OR 1·4 (0·7–3·0)	Jacobsson et al., BMJ 2003 [37]
	OR 0·7 (0·5–1·0)	Carlens et al., Ann Rheum Dis 2009 [38]
Breast feeding	OR 0·2 (0·1–0·70)	Jacobsson et al., BMJ 2003 [37]
	RR 1·0 (0·7–1·4)	Simard et al., J Rheumatol 2010 [40]
	HLA-DR4-negative; RF-positive versus RF-negative	Young et al., Ann Rheum Dis 2007 [16]
	OR 0·18 (0·04–0·99)
Early life infections	Hospitalization for any infection during the first year of life: OR 1·4 (0·8–2·5)	Carlens et al., Ann Rheum Dis 2009 [38]
	Risk of seropositivity for RF in those sharing a bedroom in childhood: OR 0·48 (0·30–0·78)	Edwards et al., Ann Rheum Dis 2006 [39]
Place of birth	Iraq versus Sweden	Li et al., Arthritis Rheum 2009 [32]
	SIR 1·55 (1·05–2·21)
	Greece versus Sweden	Li et al., Arthritis Rheum 2009 [32]
	SIR 0·31 (0·17–0·52)

HLA-DR: human leucocyte antigen D-related; RR: relative risk; OR: odds ratio; SIR: standardized incidence ratio; CI: confidence interval; RF: rheumatoid factor.