Table 3.

Association of age at first birth among parous women born after 1965 and diagnosed with primary invasive breast cancer between 2009 and 2016 in Scotland by surrogate molecular subtypes adjusted for age at diagnosis

	Luminal B-like (HER2−) (n = 707)		Luminal B-like (HER2+) (n = 440)		HER2-overexpressed (n = 169)		TNBC (n = 467)
	OR	95% CI	OR	95% CI	OR	95% CI	OR	95% CI
Age at first birth (years)
< 20	1.00	(reference)	1.00	(reference)	1.00	(reference)	1.00	(reference)
20–24	1.08	0.77–1.51	1.18	0.77–1.79	1.41	0.78–2.55	0.94	0.66–1.36
25–29	0.89	0.64–1.22	1.36	0.92–2.02	1.10	0.62–1.95	0.66	0.45–0.91
30–34	1.00	0.72–1.39	1.21	0.80–1.82	1.32	0.74–2.38	0.72	0.51–1.07
≥ 35	1.17	0.81–1.71	1.53	0.97–2.43	0.91	0.43–1.91	0.96	0.63–1.47
Age at diagnosis (years)
20–35	1.00	(reference)	1.00	(reference)	1.00	(reference)	1.00	(reference)
36–40	0.64	0.43–0.94	0.54	0.35–0.82	0.55	0.31–0.97	0.45	0.30–0.68
41–45	0.35	0.25–0.50	0.33	0.22–0.49	0.29	0.17–0.49	0.25	0.17–0.36
46–50	0.30	0.21–0.44	0.26	0.17–0.40	0.25	0.14–0.44	0.20	0.13–0.29

^*Significant at 5% level

Referent subtype used here is luminal A-like breast cancer