Identification of a genetic disorder in the fetus can lead to life-saving interventions initiated either prenatally or early in the post-natal period. Many genetic disorders are detectable in the prenatal period, and the capacity to identify them has increased remarkably as molecular genetic testing techniques continue to improve and become incorporated into clinical practice. Genetic information relevant to fetal diagnosis may be generated prior to conception, and routine prenatal screening of the parents or fetus may offer important clues that direct the fetal diagnostic genetic evaluation.