If this will be your first pregnancy, don't risk it until you're working. The first is always the hardest. The pregnancy can through emotional and physical hurdles at you at unexpected proportions. And who knows how long it will take you to recover? If you give birth with a c-section, recovery can be long. Add more recovery time if you had a c-section after a long labor. And then having a baby for the first time...you get my drift? You want to make sure that your first pregnancy, birth, and exposure to motherhood will be during a time which isn't so crucial to your career and education.
Though my natural anatomy disqualifies me from giving birth, I can honestly tell you this as my wife just gave birth three weeks ago...our first. A 37 hour labor followed by c-section - it was not pretty...lots of "firsts", accompanied by even more pain. You do not want to be in pod school or residency when this happens.
However, if this is not your first kid, you can probably guage what type of pregnancy and birth you'll have, and motherhood will not be as new anymore.