A new study has found that the more times a woman is pregnant and gives birth, the higher her chances of developing a rare but agressive type of breast cancer known as triple-negative breast cancer.

The study, published in the Journal of the National Cancer Institute, evaluated data from the Women's Health Initiative from some 150,000 postmenopausal women, more than 300 of whom went on to develop triple-negative breast cancer. They found that the number of times a woman gave birth definitely upped her chances for developing this type of cancer.

But here's the confusing part.  

Other studies have shown that in general, pregnancy and childbirth lower a womans's chances of developing breast cancer, but the risk of developing this particular type of breast cancer seems to increase with the number of pregnancies a woman has.  

Confused? Me too.

One theory is that pregnancy causes certain changes in the cellular structure of the breast that make a woman less susceptible to breast cancer. But, for women who develop triple-negative breast cancer, this change in cellular structure may actually lead to an abnormal response from breast tissue which may then lead to the development of this rare type of cancer.  

Better? Not really, I know.

Triple-negative breast cancer accounts for only 10 to 20 percent of all breast cancers, and it only came on the radar of health experts in the last 10 years. This just goes to show how little we really know about breast cancer as a whole, and how to protect women from the disease.

The opinions expressed by MNN Bloggers and those providing comments are theirs alone, and do not reflect the opinions of MNN.com. While we have reviewed their content to make sure it complies with our Terms and Conditions, MNN is not responsible for the accuracy of any of their information.