Ultrasonographic Screening for Fetal Malformations

As the risk for fetal malformation is present in all pregnant women, many experts believe that prenatal ultrasound screening should be universal. The frequency of fetal malformations and the undesirable consequences for affected infants and their families are convincing arguments for using this modality on a routine basis. When operated rigorously at certain periods of gestation, ultrasonography is the best tool to detect fetal malformations. It can show many different types of defects, sometimes very early in pregnancy. The usefulness of the screening process also depends on the technical quality of the scan, the skill of the operator, the competence of the interpreter, and the availability of options regarding malformation management. The great majority of pregnant women are at low risk for fetal malformation, and a small minority are at high risk (e.g., those with a predisposing genetic history or maternal diabetes). Both low-risk and high-risk groups can carry malformed fetuses, of course, but the numbers and proportions differ. The number of malformations is higher in low-risk gravidas than in high-risk gravidas because most pregnant women belong to the former group. In contrast, the proportion of malformations is higher in high-risk gravidas than in the low-risk group. Regardless, the risk for fetal malformation is always present among pregnant women and suggests a role for routine ultrasonographic screening. Because of the paucity of symptoms generating suspicion of malformation, ultrasonography is a very valuable tool for detecting anomalies in women whose pregnancies are otherwise uneventful.