Table 3.

Association of one’s own birthweight and future risk of rheumatoid factor positive rheumatoid arthritis in the Nurses’ Health Study (N=378)

Birthweight	RA cases	Person-years	Age-adjusted RR (95%CI)	Multivariable RR(95% CI) adjusted for Perinatal Confounders†	Multivariable RR (95% CI) adjusted for Perinatal Confounders and RA Risk Factors ††
< 2.5 kg	31	174,782	0.9 (0.6–1.4)	0.9 (0.6–1.4)	0.9 (0.6–1.5)
2.5–3.175 kg	91	495,776	1.0 (0.7–1.2)	0.9 (0.7–1.2)	1.0 (0.7–1.3)
3.2–3.85 kg	139	716,737	1.0 (ref)	1.0 (ref)	1.0 (ref)
3.9–4.54 kg	28	174,632	0.8 (0.5–1.2)	0.8 (0.5–1.2)	0.7 (0.4–1.1)
>4.54 kg	16	36,249	2.2 (1.3–3.7)	2.1 (1.2–3.5)	2.1 (1.2–3.6)
Not sure/missing	73	400,594	0.9 (0.7–1.2)	0.9 (0.6–1.3)	0.8 (0.6–1.1)

^†Adjusted for potential confounders that occurred during the perinatal period: age, maternal history of diabetes, father’s occupation at age 16, (proxy for socioeconomic status at time of birth), prematurity, history of parents’ smoking, (a proxy for fetal second hand smoke exposure), mother’s body shape at age 50, region of country lived in at birth

^††Adjusted for potential perinatal confounders above plus risk factors for RA, including pack years smoked, age at menarche, use of oral contraceptives, use of post-menopausal hormones, total lifetime breast feeding, BMI at age 18 and a history of diabetes mellitus.