Michael,

It is morally permissible to perform life-saving procedures, but not life-saving abortions.

The difference is this:

One can never directly attack the pre born child because of the bedrock principle that one can never intentionally kill an innocent human being. Therefore, when a mother's life is in danger,
only procedures that directly involve her health are permitted, if they are not a direct attack on the child's life or well being.

• For instance, the surgical removal of a portion of the fallopian tube, where an embryo is stuck, is a way of saving the mother's life if, and when, both parties are sure to die due to a burst tube; or
• the removal of a cancerous uterus before viability when both parties will die if something is not done immediately.

In these particular cases under the principle of double-effect measures can be taken to save the mother rather than allow both to die — as long as there is no direct attack on the child.

Paul