Amenorrhea or absence of menstruation in women is the first symptom of a possible pregnancy. When the period does not come on the due date and there is a delay, it is possible that pregnancy has occurred. This usually occurs in week 4 of gestation, so the pregnancy test may already be positive.
However, it is essential not to confuse implantation bleeding with a period. This bleeding is much lighter and pinkish or brownish in color. Moreover, the duration of implantation bleeding is shorter than that of menstruation.