Radek Bukowski, M.D., Ph.D., from the University of Texas Medical Branch in Galveston, and colleagues examined the risk of breast cancer in relation to a first infant's birth weight, mother's own birth weight, and breast cancer risk factors in a prospective cohort of 410 women in the Framingham Study. In a separate prospective cohort of 23,824 pregnant women, serum concentrations of estriol (E3), anti-estrogen alpha-fetoprotein (AFP), and pregnancy-associated plasma protein-A (PAPP-A) were measured.

During a median of 14 years of follow-up the researchers identified 31 women who were diagnosed with breast cancer. Compared with other women, those with infants in the top quintile for birth weight had an increased risk of breast cancer (hazard ratio [HR], 2.5; P = 0.012). The association persisted after adjustment for the mother's own birth weight and traditional risk factors for breast cancer (adjusted HR, 2.5; P = 0.021). Infant birth weight correlated strongly in a positive manner with maternal E3/AFP ratio and PAPP-A concentration during pregnancy, even after adjustment for breast cancer risk factors.

"Giving birth to an infant with high birth weight was associated with increased breast cancer risk in later life, independently of mother's own birth weight and breast cancer risk factors and was also associated with a hormonal environment during pregnancy favoring future breast cancer development and progression," the authors write.

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