ASPO Abstracts
Maternal physical activity during pregnancy and onset of breast development in their daughters in the LEGACY Girls Study cohort
Category: Lifestyles Behavior, Energy Balance & Chemoprevention, Molecular Epidemiology & Environment
Conference Year: 2018
Abstract Body:
Earlier onset of breast development (thelarche) increases risk of breast cancer, independent of age at menarche. Given the decline in age at thelarche, it is important to examine whether modifiable factors are related to thelarche. Maternal factors including pre-pregnancy body mass index (BMI) and gestational weight gain (GWG) are related to timing of their daughter’s menarche and thelarche. Less is known about whether maternal physical activity during pregnancy is related to thelarche. Using longitudinal Weibull models, we assessed whether maternal physical activity during pregnancy at home, at work and recreationally, reported by the mother at baseline, was associated with thelarche, defined as maternal report of Tanner stage 2+, in 599 girls from a prospective cohort in which approximately half of the girls have a history of breast cancer in a first- or second- degree relative (BCFH). We used maternal reports of thelarche during follow-up or recalled age at thelarche for girls that entered the cohort at Tanner stage 2+. We adjusted for age, race/ethnicity, maternal pre-pregnancy BMI and GWG, and examined mediation by daughter’s BMI-for-age percentile between ages 5-7 years. We conducted sensitivity analyses in 263 girls ages 5-7 years at baseline with prospective data only. Daughters of mothers that reported no regular recreational physical activity during pregnancy experienced earlier thelarche than daughters of highly active mothers, independent of maternal BMI (adjusted Hazard Ratio (aHR)=1.63, 95% Confidence Interval (CI)=1.09-2.45). The association between maternal inactivity during pregnancy and thelarche did not materially change after considering GWG (aHR=1.53, 95% CI 1.03, 2.27) or daughter’s BMI percentile (aHR=1.68, 95% CI 1.12-2.51). Associations were stronger in girls ages 5-7 years (aHR=1.98, 95% CI 1.14-3.45). Maternal physical activity at work or home were not associated with daughter’s thelarche. In a cohort enriched for BCFH, we found that maternal physical inactivity during pregnancy is associated with earlier thelarche in their daughters, independent of maternal BMI, GWG and childhood body size. These findings suggest that modifying physical activity during pregnancy could reduce breast cancer risk in the next generation.
Keywords: breast development, thelarche, physical activity, pregnancy, breast cancer family history