1. Prepare the patient and the transducer: The patient should be asked to empty her bladder immediately preceding the procedure. The transvaginal transducer is topped with ultrasound gel and covered with a sterile sheath, and then topped with sterile lubricant. (See Figure 2 in Chapter 33: First Trimester Ultrasound.) The transducer is gently and slowly introduced through the introitus in the sagittal plane. (See Figure 3 in Chapter 33: First Trimester Ultrasound.) After slightly compressing the anterior cervical lip, withdraw the transducer so that the cervix is not visibly compressed.

2. Identify the cervical anatomy: Visualize the cervical canal, the internal and external os, and the fetal presenting part (Figure 35-1).