Congenital Abnormalities: Prenatal Diagnosis and Screening

Congenital malformations are an important cause of prenatal, perinatal, and infant mortality and morbidity. Three percent of newborns have a single major malformation and 0.7% have multiple major defects. The frequency is much higher prenatally, the majority aborting spontaneously. During the past 50 years, infants with major anomalies have become the focus of increasing and diverse professional expertise and consume a large slice of health budgets in developed countries where their importance as a cause of perinatal mortality has grown as deaths from intrapartum problems have declined and better neonatal care has improved the survival of normally formed low birth weight babies (see Chapter 11). Clinical interest in malformations has been enhanced because sophisticated surgical and anesthetic management makes correction of some major defects possible. This and the recognition of syndromes, their mode of inheritance, and sometimes their etiology requires detailed information from the pathologist in respect to those babies who die, or where termination of pregnancy has been carried out.

There has been rapid expansion of both prenatal diagnostic and screening tests, and in the many different types of disorder that can be detected prenatally. This, and increasing interest in the pathology of the spontaneously aborted fetus, means that pathologists need to be acquainted with malformations in the fetus at an earlier stage of development than previously encountered. They must also recognize the following: that the natural history of congenital malformations is not always known; that malformations are now being defi ned earlier in gestation; that documentation of abnormalities at different stages is vital; that some disorders may have distinct, gestation-related manifestations; that a major malformation may have different etiologies and thus different recurrence risks; and that coexisting minor dysmor-phism may indicate a syndrome diagnosis or a specifi c etiology. Recognition of the difference between a collection of associated defects that may constitute a syndrome and a chain of events consequent on a single malformation resulting in a sequence of malformations or progressive deformity is important. Detailed observation of normal embryonic and fetal development and of structural abnormalities in the fetus has increased our awareness of the pathogenesis and natural history of many malformations. Our understanding of their etiology has progressed at a much slower rate.