The Basic Steps of an Obstetric Ultrasound Examination

Summary

The video demonstrates a basic second- or third-trimester obstetric ultrasound examination. It explains how to prepare the woman and equipment, follow a systematic scanning sequence, assess fetal position and pregnancy features, take standard biometric measurements, and provide aftercare.

Ultrasound can help estimate gestational age and fetal weight; assess fetal viability and presentation; locate the placenta; measure amniotic fluid; identify multiple pregnancies; and detect some fetal abnormalities.

Examination Steps

1. Prepare the Woman and Equipment

• Enter the woman’s details and confirm them with her.
• Explain the scan and its purpose, check that she is ready, and answer her questions.
• Position her comfortably—usually lying to the right of the examiner and facing them. Adjust the couch and stool for a comfortable working posture.
• Keep her covered and protect her clothing from gel. Apply gel to the lower abdomen.
• Select a probe and preset suited to the pregnancy’s gestational age and the woman’s body mass index.
• Hold the probe in the right hand and operate the machine controls with the left.

2. Check and Maintain Probe Orientation

• In a transverse view of the lower abdomen, check that the mother’s right side appears on the left of the screen. Confirm this by pressing a finger beside the probe and observing where it appears.
• In a longitudinal view, the uterine fundus should appear on the left of the screen and the maternal bladder on the right.
• Rotate the probe clockwise when changing from transverse to longitudinal, and anticlockwise when changing back.
• Keep probe orientation consistent and avoid rotating it more than 100°.
• Move the probe by sliding, rotating, dipping, or angling it.

3. Follow the Six-Step Basic Examination

The video presents a systematic sequence for a basic second- or third-trimester scan:

1. Identify the presenting fetal part. Place the probe transversely in the center of the lower abdomen, just above the symphysis. Angle it forwards and backwards to identify the part of the fetus closest to the birth canal, such as the head in a cephalic presentation.

2. Check fetal heart activity. Keeping the probe transverse, slide upwards towards the maternal umbilicus to find the fetal heart and heartbeat. If the heart is not seen, sweep to the maternal right and left. The video also recommends letting the woman view the screen.

3. Survey the uterus and check for multiple pregnancy. Sweep transversely up the right side of the uterus from the symphysis to the fundus, then repeat through the center and left side. The uterine size determines whether two or three sweeps are needed. Then rotate to longitudinal and survey from right to left, both above and below the umbilicus, keeping the probe perpendicular to the floor. This survey can show a singleton or twins.

4. Locate the placenta. In a longitudinal orientation, sweep from the right fundus down towards the symphysis along three tracks to assess placental location. If the placenta is low, move to the midline and use small movements to locate its leading edge in relation to the internal os.

5. Assess amniotic fluid. Mentally divide the uterus into four quadrants. Sweep through each in longitudinal orientation and identify the deepest vertical pocket that contains neither fetal parts nor umbilical cord. Measure each pocket with the calipers at 90° to the horizontal.

   • The amniotic fluid index (AFI) is the sum of the four measurements.
   • The deepest vertical pocket (DVP) is the largest one.
   • Watch for reverberation artifacts, which can lead to underestimation.

6. Take fetal biometric measurements. The video combines a first fetal sweep with selected planes from ISUOG’s “20 planes and two sweeps” approach. It recommends taking each measurement at least three times to check consistency and saving each measured image.

4. Take Biometric Measurements

• First fetal sweep: Rotate the probe to obtain a longitudinal section and identify the fetal head and the long axis of the body.
• Head measurements—BPD and HC (plane 4): From the fetal longitudinal axis, rotate 90° at the head. Adjust the probe to obtain the correct head shape and intracranial landmarks for the transventricular plane.
  • Measure the biparietal diameter (BPD) at the widest point across the skull. Depending on local charts, use either outer-to-outer or outer-to-inner caliper placement.
  • Measure the head circumference (HC) with the ellipse along the outer edge of the skull.
• Transcerebellar diameter (TCD; plane 6): Rotate towards the fetal neck while keeping the cavum septum pellucidum in view to obtain the transcerebellar plane. Measure the maximum diameter of the cerebellum with linear calipers.
• Abdominal circumference (AC; plane 11): Rotate back to the transventricular plane and slide down through the chest, where the heart can be seen (plane 7). Continue towards the abdomen, using small rotations or angling movements as needed to maintain a transverse section. At plane 11, identify the stomach and a small central portion of the umbilical vein. Measure the AC with an ellipse along the outer edge of the abdomen.
• Femur length (FL): From the abdominal plane, slide down towards the fetal pelvis and rotate to view the femur longitudinally. This helps avoid measuring the humerus instead. Measure the longest visible diaphysis, placing calipers at its ends, aligning them with the bone’s long axis, and excluding spur artifacts.

5. Complete the Examination and Provide Aftercare

• Clean the probe and return it safely to its holder.
• Clean the woman’s abdomen, help her sit up, and wash hands.
• Check the measurements in report mode.
• Explain the results, invite questions, and provide a handwritten or printed report for the woman to share with her caregiver.
• End the examination and clear the woman’s information from the screen before preparing for the next scan.

Speakers and Sources Featured

• Instructional narrator/voiceover: Provides the scanning guidance; no individual speaker is named in the subtitles.
• ISUOG: Cited for the six-step approach and the standardized “20 planes and two sweeps” approach. It is mentioned as a source, not heard speaking in the subtitles.
• Medical Aid Films: Identified as the video’s channel or publisher in the metadata.