Chapter 6. Use of Ultrasound in the Prenatal Diagnosis of Congenital Disorders

Abstract

This chapter discusses the use of ultrasound in the prenatal diagnosis of congenital disorders. Ultrasound and fetoscopy are both valuable techniques in the diagnosis of fetal defects. They should not be regarded as mutually exclusive techniques because, used in a complementary way, they can be most effective. Fetoscopy permits direct visualization of external fetal structures and the identification of fetal vessels on the placental surface suitable for fetal blood sampling. Short pulses in the region of 1 ps are transmitted into the maternal abdomen where they are gradually attenuated by absorption, refraction, or reflection from tissue interfaces. The reflected echoes are received by the same transducer during the silent period of about 3 ms between emitted pulses. The uterus is first scanned to localize and define accurately a pool of amniotic fluid, and a route to it avoiding fetus and placenta is chosen. The depth of the pool and its distance from the maternal skin can be measured by electronic calipers on the B-mode display to ensure that the needle chosen is long enough or that it is not inserted too deeply.