The process of child birth is really painful.
Mothers feel a lot of pain during childbirth. And the whole process of birth takes a lot of time, sometimes hours.
When baby is ready to come out, in case of human after 9 months of gestational period (the time spent inside mom's womb), mother's uterus starts to contract. These contraction increases in intensity and duration with time. At a point the mouth of uterus (cervix) opens and baby comes out.
This whole process of contraction of muscles of uterus is very painful. Mothers go through this pain for hours (sometimes 12 hours or more).
But as women are so patient and babies are so amazing that there are more than seven thousand million people in the world.
And with the advancement of science doctors now can mitigate the pain of childbirth. Although in third world countries moms are not so lucky.