Answer:
   
   Jewish Law has traditionally opposed birth control or abortion when
   practiced for purely selfish reasons. The first mitzvah we find in the
   Torah is to have children, to "be fertile and increase". Judaism
   believes that a home without children is a home without blessing.
   However, Judaism also believes that as long as a couple is planning to
   have children, the concept of planned parenthood or spacing of births
   does not constitute a religious problem in Judaism. Judaism is more
   concerned with the birth control method used; in particular, some
   methods are not permitted because of the injunction against "the
   destruction of seed." For example, contemporary Orthodox rabbinical
   authority has expressed no objection to the use of the "pill". Still,
   the use of condoms is forbidden, as are some uterine devices. [Note
   that, for traditional Jews, the use of condoms with respect to the
   AIDS crisis is not an issue, for sex is permitted only within a
   monogamous marriage.]
   
   It is also true though, that traditionally Judaism has encouraged
   having many children. Some of this is based on the argument that,
   after the Holocaust, Jews should not avoid having children. The
   minimum number of children one must have to fulfill the Mitzvah "to be
   fertile and increase" is a matter of rabbinic dispute. Some rabbis say
   that one must have at least two children, and some say at least one of
   each sex.
   
   With respect to the liberal movements, such as Reform Judiasm: Again,
   birth control or abortion is opposed when practiced for purely selfish
   reasons. Birth control are accepted under certain conditions such as
   where pregnancy represents a health hazard to the mother or child, or
   when previous children have been born defective. Liberal judaism
   extends this concept to include extreme poverty, inadequate living
   conditions and threats to the welfare of existing children in the
   family. The Central Conference of American Rabbis (Reform) goes so far
   as to declare that birth control is a necessity under certain family
   conditions. Most Reform and some Conservative rabbis subscribe to the
   program of planned parenthood. Liberal judaism has no problem with the
   use of condoms.
   
   A closely related issue is that of therapeutic abortion, prescribe by
   a physician to save the life or health of a pregnant woman. In Jewish
   law such an action is considered entirely justified. The life of the
   mother, Jews believe, is more important than that of a child not yet
   born, both to her husband and to any other children she might have.
   
   In Judaism, if a woman is pregnant, and she finds out that there is a
   possibility that either she or the baby is will die if the pregnancy
   continues, then the woman must have an abortion. Of course, rarely is
   the risk so cut-and-dry. In practice, one has to assess the odds of
   each course of action. If one can, a doctor and a Rabbi should be
   consulted. In case of doubt, such as an emergency where one can't
   spend time looking for one's Rabbi, the mother's life takes
   precedence.
   
   Abortion before 40 days gestation is prohibited, but is not considered
   murder. There are numerous issues that override the prohibition. For
   example, the sanity (not just the happiness, but actual competency) of
   a rape victim. This too has to be evaluated by a Rabbi and a doctor
   (and a psychologist) to see exactly how much is at risk.
   
   The most important consideration in both questions is: what is the
   best for the entire family? The sanctity of marriage is not in
   reproduction. It is in the bond that exist between husband, wife and
   the children they want and love.