There are many ethics texts that deal with theories and issues. Of these, I recommend Vardy's Puzzle of Ethics and Bowie's Ethical Studies. However, wider reading is essential, particularly with the ethical issues. I hope the reviews below are helpful in choosing where to invest your time:
Book Rating/5 Cover Rethinking Life and Death , Peter Singer - A hugely influential contemporary utilitarian. The book is a good read, but hard to dip into. p208 onwards (just after Singer rewrites the 10 commandments) relate to abortion and (p210ff) aborting a foetus with Down's Syndrome.
Issues of Life and Death Michael Wilcockson - A useful chapter (24 pages) on abortion, although a bit hit and miss. Covers a lot of ground and includes some useful statistics.
