A bit more information - as most rape victims will not immediately become pregnant prior to their getting attention at a hospital (performance of a rape kit exam):
"In 2001 the U.S. Conference of Catholic Bishops issued their revised “Ethical and Religious Directives for Catholic Health Care Services”. Directive 36 states:
“
A female who has been raped should be able to defend herself against a potential conception from the sexual assault. If after appropriate testing, there is no evidence that conception has occurred already, she may be treated with medications that would prevent ovulation, sperm capacitation, or fertilization. It is not permissible, however, to initiate or to recommend treatments that have as their purpose or direct effect the removal, destruction, or interference with the implantation of a fertilized ovum”. [1]
The Directive does not specify what constitutes “appropriate testing” or “evidence that conception has occurred”. Consequently, Directive 36 has been subject to different interpretations.
One school holds that giving women a pregnancy test followed by a “morning-after pill” if the test is negative is morally permissible and in line with Directive 36. As pregnancy testing, at present, can only reveal a pregnancy prior to any recent rape, and not whether a recent rape has itself resulted in pregnancy, this school holds, for reasons laid out below, that the only relevant factor to consider before giving a morning-after pill is whether the woman patient has a prior-to-rape pregnancy which would be endangered by the administration of a pill.
Opposed to this school is the ovulation-testing school, which insists that, as well as a pregnancy test, a simple urine dipstick test together with any personal data on the woman’s ovarian cycle stage[2] should be obtained in order to assess whether a) “emergency contraception” can be appropriately used to prevent ovulation or sperm capacitation, and b) whether such “emergency contraception” will be at all necessary in a given case. This approach aims to avoid giving unnecessary and potentially dangerous drugs to women, and further aims to take seriously the possibility that drugs administered at mid-cycle or early post-ovulatory phases could endanger the life of a newly conceived child."
continues at:
linacre.org/MornAftPillMcC.htm