Obstetric Ultrasound

Abstract

The major goals of the first trimester ultrasound examination are to determine fetal viability and to establish if the gestation is intrauterine in location. The transabdominal examination is performed through an optimally distended urinary bladder, usually achieved by maternal ingestion of 4–6 glasses of water, 30–40 minutes prior to the examination. Sagittal, transverse and oblique scans are obtained through the uterus and adnexa with an internally focused 3.5 or 5.0 mHz transducer. Real-time sector transducers, either mechanical or annular, are best suited to imaging early gestations transabdominally, as they can be angled to allow for variation in uterine and adnexal position. Occasionally, a linear transducer may give superior anatomic detail of fetal structures during the first trimester.