biostudies-literatureGoldberg MBreast Cancer Research FoundationAnne and Max Tanenbaum Chair in Molecular Medicine at the Sinai Health SystemNational Cancer InstituteNCI NIH HHSNational Institutes of HealthUniversity of TorontoCanadian Breast Cancer Foundation272-283https://www.ebi.ac.uk/biostudies/studies/S-EPMC9908055biostudies-literatureUnknown52(1)<h4>Background</h4>Earlier onset of breast development (thelarche) is associated with increased breast cancer risk. Identifying modifiable factors associated with earlier thelarche may provide an opportunity for breast cancer risk reduction starting early in life, which could especially benefit girls with a greater absolute risk of breast cancer due to family history.<h4>Methods</h4>We assessed associations of maternal pre-pregnancy body mass index (BMI), physical activity during pregnancy, gestational weight gain and daughters' weight and length at birth with age at thelarche using longitudinal Weibull models in 1031 girls in the Lessons in Epidemiology and Genetics of Adult Cancer from Youth (LEGACY) Girls Study-a prospective cohort of girls, half of whom have a breast cancer family histInternational journal of epidemiologyMaternal and prenatal factors and age at thelarche in the LEGACY Girls Study cohort: implications for breast cancer risk.PMC9908055K01 CA186943R01CA138819R01 CA138822R01 CA138844R01 CA138819R01CA138822R01CA138844K01CA186943R01 CA138638R01CA138638Houghton LCKeegan THMKnight JAAndrulis ILWei YFrost CJChung WKBradbury ARBuys SSTerry MBMcDonald JASchwartz LADaly MBGoldberg MJohn EMfalseMaternal and prenatal factors and age at thelarche in the LEGACY Girls Study cohort: implications for breast cancer risk.<h4>Background</h4>Earlier onset of breast development (thelarche) is associated with increased breast cancer risk. Identifying modifiable factors associated with earlier thelarche may provide an opportunity for breast cancer risk reduction starting early in life, which could especially benefit girls with a greater absolute risk of breast cancer due to family history.<h4>Methods</h4>We assessed associations of maternal pre-pregnancy body mass index (BMI), physical activity during pregnancy, gestational weight gain and daughters' weight and length at birth with age at thelarche using longitudinal Weibull models in 1031 girls in the Lessons in Epidemiology and Genetics of Adult Cancer from Youth (LEGACY) Girls Study-a prospective cohort of girls, half of whom have a breast cancer family hist2023-01-01T00:00:00Z2023 Feb2025-05-29T16:23:04.798Z2025-05-29T16:23:04.798ZS-EPMC99080553561301510.1093/ije/dyac108