Heavier placentas/babies increase breast cancer risk for mom

Women who develop heavier placentas during pregnancy have a higher risk of breast cancer, according to the results of a population-based cohort study from Sweden.

Researchers looked at how a number of pregnancy characteristics influenced the risk of breast cancer in a cohort of over 300,000 women. They found that compared with women whose placentas weighed less than 500 g in two consecutive pregnancies, the risk of breast cancer was almost doubled (adjusted hazard ratio, 1.82) in women whose placentas weighed between 500 and 699 g in their first pregnancy and at least 700 g in their second pregnancy (or vice versa) and was slightly more than doubled (adjusted hazard ratio, 2.05) in women whose placentas weighed at least 700 g in both pregnancies.

Other first-birth factors found to be associated with a higher risk of maternal breast cancer included delivering an infant weighing 4,500 g or more, delivering at 42 weeks or later, greater maternal age, and greater maternal height. Women with body mass indices of 29 or higher and women who smoked during pregnancy had lower rates of breast cancer than counterparts.

Cnattingius S, Torrang A, Ekbom A, et al. Pregnancy characteristics and maternal risk of breast cancer. JAMA. 2005;294:2474-2480.