Stress
You're basically a firefighter who happens to rescue babies in hospital wards instead of cats in trees. As an emergency first-responder to all problems baby-related, your job's both physically exhausting and emotionally taxing.
If you're a particularly busy midwife, the work may be non-stop. You're on your feet for twelve hours at a time, rushing from one patient to another in a labor ward filled to capacity. If you get tired, you can't sit down to rest your legs for a while. If you get cranky, you can't take it out on your patients. And it's not like the baby's going to wait while you hit the restroom.
And sometimes, you'll have to get through a lot more than that. Midwives exist because pregnancies and deliveries sometimes have complications. Even in today's world, not all those complications get resolved for the best.
Be prepared for some sad, tragic, awful, and awfully stressful moments in your job. It's just a part of it—but if you've seen The Lion King, you already know a little bit about the circle of life (it moves us all).
Sorry in advance for getting that stuck in your head.