Genetic Counseling and Genetic Screening

major congenital anomaly. About one half of these anomalies are detected at birth; the remainder becomes evident later in childhood or, less often, adulthood. Although nongenetic factors may cause malformations, genetic factors are usually responsible. In addition, more than 50 percent of fi rst-trimester spontaneous abortions and at least 5 percent of stillborn infants have chromosomal abnormalities (see Chapter 24). Given such a pivotal role for genetic factors, medical genetics becomes integral to the practice of modern obstetrics. This chapter considers the principles of genetic counseling and genetic screening. Disorders amenable to genetic screening and prenatal diagnosis are enumerated. Genetic Counseling and Genetic Screening