Table 2. Association between history of GDM and incident invasive breast cancer risk.

	No GDM HR (95% CI)	GDM HR (95% CI)	p-value
Cases – no.	2,277	100
Person-years*	923,694	58,384
Age-adjusted	1.00 (reference)	0.68 (0.55, 0.84)	0.0003
Multivariable adjusted	1.00 (reference)	0.68 (0.55, 0.84)	0.0004

HR=hazard ratio, CI=confidence interval

^*Person-years are calculated as the time from age at first birth or first GDM pregnancy, through end of follow-up (the date of incident breast cancer diagnosis, death, or last questionnaire return through May 31, 2013)

Multivariable model additionally adjusts for body mass index at age 18 (continuous), weight gain since age 18 (continuous), height (continuous), total physical activity (MET-hours/week, quintiles), alcohol intake (none, 1-14 grams/day, ≥15 grams/day), age at menarche (≤10 years old, 11-12, 13-14, ≥15), birth index (continuous), total breastfeeding (none, <6 months, ≥6 months), menopausal status (premenopausal, postmenopausal, unknown), hormone therapy use (never, ever use of estrogen + progesterone, past – estrogen only or other, current – estrogen only or other), family history of breast cancer in mother or sister (yes/no), personal history of benign breast disease (yes/no), White race/ethnicity (yes/no), and mammography within the past 2 years (<40 years old, ≥40 and no mammography, ≥40 and mammography for screening, ≥40 and mammography for abnormality/symptoms).