The ban on abortion remains absolute, although the Roman Catholic bishops of England and Wales have decided that the so-called morning-after pill may also be used by rape victims in certain circumstances.
An article in the Jesuit magazine Civillta Catolica, which is approved before publication by the Vatican, argues that contraception is a legitimate form of self-defence for a rape victim. The author, Fr Giacomo Perico, says that rape is an act of violence, to which the rules applying to an act within marriage cannot apply.
'In this particular situation, it is legitimate to use contraception to avoid a possible pregnancy. It is not then a refusal of a gift of love, but a form of legitimate self-defence.'
The ban on artificial contraception within marriage restated by Pope Paul VI 25 years ago in the encyclical Humanae Vitae has been widely ignored in the West.
The article in Civillta Catolica makes it plain that nuns in the Belgian Congo had been allowed to use contraceptives in the early Sixties when they were in danger of rape. The author argues that such concessions cannot be extended solely to nuns.
Luke Gormalley, the director of a Roman Catholic research centre in medical ethics in London, says that the Vatican's teaching is perfectly consistent. 'The teaching about the wrongness of contraceptive intercourse is about a chosen sexual activity. It is not a mechanistic prohibition of certain substances.
'But when you're talking about rape, you're not talking about chosen sexual activity at all. If she takes contraceptives, the woman is then defending herself against an extension of male violation.'
However, opponents of Humanae Vitae have seized on this as a crucial weakening in the Vatican's general prohibition of birth control. If a woman is allowed to use contraception to protect herself from the psychological harm of bearing a rapist's child, as Civillta Catolica argues, then why should she not be allowed to use it to prevent other damage?
Mr Gormalley said that if a woman believes that she may ovulate after a rape, then she can take a 'morning after' pill to inhibit ovulation but not as a form of very early abortion.