Describes the use of combined biochemical markers to screen for neural tube and chromosomal defects, presents the latest developments relating to testing fetal cells in the mother's blood, and reviews major advances in molecular genetics that permit prenatal carrier detection and presymptomatic and predictive testing. Much has changed since the publication of the fourth edition. The new technologies of fetal MRI, 3-D ultrasound, and real time PCR of fetal DNA in maternal circulation yield crucial information, while integrated screening of data from the first and second trimesters coupled with ultrasound now produces a 94 percent detection rate.