This article is from the Pregnancy Screening FAQ, by Lynn Gazis-Sax (firstname.lastname@example.org) with numerous contributions by others.
In most cases, prenatal treatment is not available, and prenatal testing
is used to give parents a choice of whether to continue the pregnancy or
have an abortion, or to give parents an opportunity to prepare to care for
a child with a disability. In some cases, prenatal diagnosis can also
affect medical treatment. First, while prenatal treatments are rare and
often experimental, there are prenatal treatments for some problems. For
example, fetal surgery can be done for diaphramatic hernia and complete
bladder obstruction, steroid hormones can be given before birth for
congenital adrenal hyperplasia, biotin dependence and MMA (methylmalonic
acidemia), both life threatening, can be detected and treated in the womb.
More commonly, prenatal diagnosis can be useful at delivery time. In
particular, there is some evidence that children with spina bifida can
benefit from being delivered by scheduled C-section. A study published in
the New England Journal of Medicine on March 7, 1991 indicates that babies
with spina bifida may be much less likely to be paralyzed if delivered by
C-section. 16% of the babies in the study who were delivered vaginally or
by C-section after labor had begun had no paralysis. But 45% of the
babies delivered early by C-section had no or minimal paralysis. This may
translate into whether or not children walk.
From Robbrenner@aol.com (Robert Brenner MD):
2c. Early detection can be of benefit with all types of birth defects
in giving the couple the option to either terminate the pregnancy or
prepare for the delivery of an affected child. Anencephaly is
incompatible with life so that termination is quite reasonable. In
those couples who object to termination, they can consider organ
donation after the baby is born. Many chromosomal anomalies are also
incompatible with life beyond 1 year of age (trisomy 18). There are
also many structural defects such as diaphragmatic hernia,
encephalocele, meningomyelocele, hydrocephalus, various cardiac and GI
abnormalities where delivery in a tertiary care center with pediatric
surgery available will benefit the baby. Please be aware that this
list is far from complete but these are just a few common examples.