Here's a little about it:
The global gag rule (also known as the Mexico City Policy) denies federal funding to any family planning organizations internationally that provide abortions in cases other than life-threatening emergencies or rape, provide counseling services that include abortion as an option, or lobby for increased abortion rights within the country they are working in.
This greatly affects the health care community-- for example, in Kenya (according to globalgagrule.org) eight clinics were closed and many reproductive heath care staff and programs throughout the country were cut. This in and of itself is too bad, but even more crucial is the fact that many of those closed clinics were the only place to obtain health care in their local communities.
Impacts of the Global Gag Rule on individual countries around the world here.