[Prenatal diagnosis of developmental congenital malformations--the limitations of ultrasound scanning].
Prenatal diagnosis of congenital malformations is a major goal of obstetric sonography. Although significant progress has been made in the ability to detect fetal anomalies by ultrasound, some fetal anomalies cannot be detected during second trimester routine ultrasound scanning. Among the "undiagnosed anomalies" are many fetal anomalies that follow a developmental course in-utero and have a late-onset sonographic appearance, and hence cannot be diagnosed early in pregnancy or during the traditional mid-second trimester scan. Several mechanisms cause in-utero development of fetal malformations, and the developmental course of each fetal anomaly depends on the cause, mechanism, extent and timing of the insult. In some cases the destructive or disruptive event might occur at a relatively advanced gestational age and thus go undiagnosed. Some malformations are the result of an early insult but are manifested and detected late, while others have a "late onset". This concept of the developmental natural course of fetal anomalies in-utero, must be recognized and lead to a new nomenclature for fetal malformations. In this review we describe some developmental fetal malformations and discuss the clinical, diagnostic and medicolegal implications.