Four stage in which abortion cannot be done.

Fourth trimester.

Explanation:

Fourth trimester is the fourth stage in which abortion can not be done because the baby is big enough in size and comes out from the womb. The abortion in this stage can put the life of the mother in danger so that's why abortion is not allowed. Newborn babies are learning to adjust itself to life outside the womb where it was warm so we can say that  fourth trimester is the stage in which abortion is risky and dangerous.

to this answer it would be edge enhancement

other quantities, called derived quantities, are defined in terms of the seven base quantities via a system of quantity equations. the si derived unitsfor these derived quantities are obtained from these equations and the seven si base units.