A worrisome new study came out this week in the medical journal Fertility and Sterility -- the research looked at the incidence of breast cancer in women who'd had in vitro fertilization (IVF) with those who had not the fertility procedure. In particular, the study looked at young women -- ages 20 to 44 -- in Australia and included over 21,000 women who were followed for years. Of those, about 7,400 had IVF; the rest did not.
The study found that overall there wasn't an increase in breast cancer rates in women who had IVF, but that young women who'd had IVF starting at a very young age -- at age 24 -- had a one-and-a-half-times increased risk for the disease. Comparatively, women who had IVF at the age of 40 had no increased risk.
The link may be related to a long-known connection between higher estrogen rates (women who undergo IVF are given high doses of estrogen to encourage conception and pregnancy,) and a higher risk of breast cancer. In addition to the estrogen a woman has circulatingin her body, the hormone is also found in oral contraceptives and hormone replacement therapy. The study noted that during a round of IVF, a woman's estrogen level could peak at around 4,000 pg/ml, whereas a normal level is 300 pg/ml, though estrogen is elevated only for a short time during an IVF cycle. (The study didn't have information about specific dosages for fertility drugs, though.)
The study also confirmed a well-established link between breast cancer risk and age of delivering a first baby -- which is that the older a woman is when she has her first child, the greater her cancer risk. This research found a two-fold increase in risk for women who had their first baby at age 35 or older. On the other side, having twins or higher-order multiples seems to lower risk of breast cancer.
