Pregnancy causes increased levels of estrogen to circulate in the mother's blood.
Increases in circulating estrogen have been associated with more aggressive breast cancers. Doctors are also concerned that the chemotherapy used to treat breast cancer may be damaging to the fetus. The study followed 22 women and their babies over an eight-year period. The researchers also found little to no differences in the survival rates of pregnant and non-pregnant breast cancer patients, indicating that the increases in estrogen levels does not affect the outcome of breast cancer. According to this study, mastectomy, radiation therapy, and mammography do not have a negative impact on the fetus' health.