The previous considerations apply to pregnancy that has been demonstrated by missed menses and a positive pregnancy test, a situation clear to all women. Before this well-defined state, even if the biological steps are known, there is still confusion and ignorance as to when pregnancy begins. As a result, the vocabulary used to define the possible antihormonal interventions during the processes establishing pregnancy needs to be clarified.
If menses does not occur and a pregnancy test is positive, interruption is clearly defined as abortion. However, vacuum aspiration practiced very early, within approximately two weeks of menses delay, is called ''menses regulation" (e.g., officially in Bangladesh and Turkey) or menstrual induction, and can be considered as contragestive. On the other hand, any maneuver inhibiting fertilization is called contraception, for contra conception. The word conception is generally understood as fertilization; this is wrong etymologically, since concipire (Latin) means to retain (originally retain sperm and mother blood in the uterus to make the child).
Contraception is, therefore, commonly understood as a method to preclude fertilization, for instance, by suppression of ovulation or preventing sperm from reaching the ovum. However, physicians also designate as contraceptives methods that are applied before implantation is completed. They argue that a fertilized ovum that is not implanted after in vitro fertilization does not define a pregnancy. In fact, the available pregnancy tests are based on the measurement of human chorionic gonadotropin, produced by the embryonic chorion, which passes into the woman's blood and occurs only after implantation has been initiated. Intrauterine devices (IUDs) can be defined as "contraceptive" tools because they work, in part, as anti-implantation agents. The word post-coital contraception is also largely accepted and applies to a possibly fertilized ovum. Note also that the process of implantation is not instantaneous and takes several days during the last week of the fertile menstrual cycle, just before the time at which menses would occur. Coincidentally, the development of the embryo is characterized by the streak (a marker indicating that an individual embryo has been formed, and there is no further risk of twins), which should occur at approximately the same time—about 15 days after fertilization. Before that time, not only may genetic abnormalities or defects of implantation stop the process leading to pregnancy, but the very definition of a single potential person cannot be rigorously applied. In short, during the period between fertilization and the time at which menses should occur, interrupting methods are contragestive, differing from both abortion and contraception as defined above, and not hiding the fact that they oppose pregnancy.