Table 2.

Summary of meta-analysis results for case–control/cohort studies (n=42 studies)

Reproductive factors	Contrast	Luminal A/ ER + , PR + , HER-	Luminal B/ ER + , PR + , HER +	HER2-overexpressing/ER-, PR-, HER +	Triple Negative/ basal-like/ER-, PR-, HER-
Age at menarche (n = 29)	Later vs. earlier	S-	NO	NO	S-
Age at menopause (n = 13)	Later vs. earlier	S +	S +	S +	NS +
Menopausal status (n = 7)	Post vs. pre/peri	S-	S-	NS +	NS-
Age at first birth (n = 28)	Nulliparous/later vs. earlier age at FB	S +	S +	S +	NS +
Parity (n = 29)	Higher parity vs. low/nulliparity	S-	S-	NS-	NS +
Breastfeeding (n = 30)	Ever /longer vs. never/shorter	S-	S-	S-	S-
OC use (n = 15)	Ever/longer vs. never/shorter	NS +	NS +	NS +	S +
HRT (n = 13)	Ever/longer vs. never/shorter	S +	S +	NS +	NS +

Abbreviations: S- Significant lower risk, S+ Significant higher risk, NS+ Non-significant higher risk, NS- Non-significant lower risk, NO No difference (0.95 < RR < 1.05 and NS), FB First birth, OC Oral contraceptive

HRT Hormone replacement therapy, HER2 Human epidermal growth factor receptor 2