Table 2.

Prenatal/neonatal factors and PD in the NHS and HPFS cohorts combined

Variable	# Participants*	# Cases*	Age-adjusted Rate Ratio and 95% CI.		Multivariate-adjusted† Rate Ratio and 95% CI
Birthweight (lbs)
<5.5 lbs	8932	28	0.88	0.59, 1.30	0.89	0.60, 1.31
5.5–8.4	69678	261	1.0 (ref)		1.0 (ref)
8.5–9.9	11857	43	0.83	0.60, 1.16	0.84	0.61, 1.17
10+ lbs	3417	22	1.06	0.68, 1.66	1.12	0.72, 1.74
			test for linear trend	P=0.81‡	test for linear trend	P=0.91‡
Season of birth
Spring	42335	157	1.31	0.98, 1.76	1.30	0.97, 1.74
Summer	44630	175	1.41	0.89, 2.25	1.42	0.88, 2.29
Fall	44299	173	1.26	0.94, 1.70	1.27	0.94, 1.71
Winter	41459	153	1.0 (ref)		1.0 (ref)
Handedness
Left	8290	40	1.31	0.86, 1.98	1.31	0.84, 2.06
Right	113070	494	1.0 (ref)		1.0 (ref)

^*For each factor, the number of cases and participants may not add up to the total number in the study due to missing values

^†Controlling for age in months, calendar year, PMH use, quintile of caffeine consumption, the interaction between PMH use and caffeine consumption, pack-years of smoking, and family history of PD (for NHS only)

^‡No significant non-linear trend observed