Scientists in Germany have discovered what is perhaps the only positive change in a woman's body after having kids. It has to do with our stem cells.
Women who have kids--especially if they have kids while young--have less risk of getting breast cancer later in life, and that protective effect only gets stronger with more children. (Here's more on that effect from the National Cancer Institute.)
At the same time, scientists have found that many cancers originate in the tissue's stem cells. Thinking the pregnancies and the stem cells might be connected, the German scientists compared the genes that were active in breast stem cells of mice that have had litters and mice that have not. Mice also have lower rates of breast cancer with pregnancies, so presumably their work will translate to people. The researchers published their work in the April 29 issue of Breast Cancer Research.
What the group found is in the breast stem cells of mice that have had litters, genes that are involved in cancer formation and in cell division were less active. Remember that in the cell, active genes are what are responsible for proteins being made in the cell. If their findings in the stem cells were true, they'd expect to see less of the protein as well. When they looked, they found that the protein made by one of the key genes was also reduced in the breast tissue of the mice that had had litters.
The authors of the paper go on to say that reducing the amount of this protein in the breast stem cell might be one way of protecting against breast cancer. Of course, getting from this kind of very basic discovery to something that can help people is a long road, but you don't get to the end of that road if you don't have a discovery like this as a starting point.
The National Cancer Institute has more about the different factors that appear to alter breast cancer risk. Our fact sheets have more information about the stem cell agency's funding of cancer research.