Dignitas Personae

The Vatican's first authoritative statement on reproductive science in 21 years, Dignitas Personae, approved by the Pope on June 20 and published on December 8 by the Congregation for the Doctrine of the Faith, has triggered intense debate about some of the most contentious issues in surrounding procreation, including stem cells, designer babies, cloning, and a host of techniques widely used as birth control and to help infertile couples have children.

Links for summary and Q&A: United States Conference of Catholic Bishops

Regarding what weight this carries for Roman Catholics, the following statement is made in the Vatican Summary:

The document is an Instruction of a doctrinal nature, published by the Congregation for the Doctrine of the Faith and expressly approved by the Holy Father, Pope Benedict XVI. The Instruction therefore falls within the category of documents that "participate in the ordinary Magisterium of the successor of Peter" (Instruction Donum veritatis, n.18) and is to be received by Catholics "with the religious assent of their spirit" (Dignitas personae, n.37).

Especially of interest is the following excerpt (emphasis mine), which doesn't beat around the bush the way some do regarding abortifactient methods of birth control (i.e. IUDs and all hormonal contraceptives such as the Pill and so-called "emergency contraception"):

23. Alongside methods of preventing pregnancy which are, properly speaking, contraceptive, that is, which prevent conception following from a sexual act, there are other technical means which act after fertilization, when the embryo is already constituted, either before or after implantation in the uterine wall. Such methods are interceptive if they interfere with the embryo before implantation and contragestative if they cause the elimination of the embryo once implanted.

In order to promote wider use of interceptive methods,[43] it is sometimes stated that the way in which they function is not sufficiently understood. It is true that there is not always complete knowledge of the way that different pharmaceuticals operate, but scientific studies indicate that the effect of inhibiting implantation is certainly present, even if this does not mean that such interceptives cause an abortion every time they are used, also because conception does not occur after every act of sexual intercourse. It must be noted, however, that anyone who seeks to prevent the implantation of an embryo which may possibly have been conceived and who therefore either requests or prescribes such a pharmaceutical, generally intends abortion.

When there is a delay in menstruation, a contragestative is used,[44] usually one or two weeks after the non-occurrence of the monthly period. The stated aim is to re-establish menstruation, but what takes place in reality is the abortion of an embryo which has just implanted.

As is known, abortion is “the deliberate and direct killing, by whatever means it is carried out, of a human being in the initial phase of his or her existence, extending from conception to birth”.[45] Therefore, the use of means of interception and contragestation fall within the sin of abortion and are gravely immoral. Furthermore, when there is certainty that an abortion has resulted, there are serious penalties in canon law.[46]

I found it interesting that the document takes the position that vaccines which have been developed using cells from aborted fetuses are acceptable, while questioning the morality of adopting embryos to give them life through implantation. They warn that the latter action could help perpetuate the creation of more embryos. Here's the document's statement:

According to this criterion, the use of “biological material” of illicit origin would be ethically permissible provided there is a clear separation between those who, on the one hand, produce, freeze and cause the death of embryos and, on the other, the researchers involved in scientific experimentation.