The major event that occurs during the first stage of birth is

(a) dilation of the cervix.

(b) delivery of the foetus.

(c) bursting of the membranes.

(d) expulsion of the afterbirth.

A) dilatation of the cervix

From that list, the first event is almost always dilation. It's followed

by bursting, delivery, and expulsion of the placenta.

In a small fraction of cases, the bursting may occur before dilation.