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Women experience vulnerable stages in the life cycle based upon unfolding of internal biological and psychological factors which may operate to make a woman susceptible to unwanted pregnancy. These stages occur during 1) early adolescence, 2) the period of first sexual activity, 3) involvement with one man in an ongoing stable sexual relationship, 4) times of geographic mobility, 5) the time just prior to and just following marriage, 6) postpartum period, 7) at the end of child bearing period and during the menopause. In the first two stages, contraceptive vigilance has not yet been established. In the other stages, separation or conflict may also contribute to the relaxation of vigilance.
Warren B. Miller (Mon,) studied this question.