Overview
This lecture covers the use of ultrasound in obstetric care, detailing preparation, scanning technique, measurement protocols, and post-scan care.
Uses of Obstetric Ultrasound
- Accurately estimates gestational age.
- Determines fetal viability and presentation.
- Identifies placental position.
- Measures amniotic fluid and estimates fetal weight.
- Detects multiple pregnancies and some fetal abnormalities.
Preparation for Ultrasound Scanning
- Confirm patient details and explain the scan procedure.
- Position the woman on her back, covered and comfortable.
- Apply gel to the lower abdomen.
- Choose probe and settings based on gestational age and BMI.
Standardized 6-Step Ultrasound Approach
- Start with the probe transversely above the pubic symphysis to identify fetal presenting part.
- Slide the probe to locate the fetal heart and confirm heartbeat.
- Perform sweeps in the center, right, and left uterus to fully survey.
- Rotate to longitudinal plane; slide side-to-side above and below the umbilicus.
- Check for single or multiple fetuses and assess placental location.
- Divide the abdomen into quadrants to measure deepest amniotic fluid pockets for AFI.
Measurement Techniques (ISSUOG 20 Planes & Two Sweeps)
- Take biometric measurements (BPD, HC, TCD, AC, FL) at least three times each.
- Obtain Biparietal Diameter (BPD) at the skull’s widest point—outer-to-outer or outer-to-inner.
- Measure Head Circumference (HC) using ellipse caliper around the skull.
- Measure Transcerebellar Diameter (TCD) at the cerebellum’s widest point.
- Measure Abdominal Circumference (AC) at the level of the stomach and umbilical vein.
- Measure Femur Length (FL) along the longest visible axis of femur.
Post-Scan Care and Reporting
- Clean the probe and patient’s abdomen.
- Wash hands and review scan results.
- Explain findings to the woman and answer questions.
- Provide a report for the caregiver.
- Clear patient data and prepare for the next scan.
Key Terms & Definitions
- Gestational Age — the age of the pregnancy calculated from the last menstrual period or ultrasound.
- AFI (Amniotic Fluid Index) — total depth of amniotic fluid in four uterine quadrants.
- BPD (Biparietal Diameter) — measurement of fetal head width.
- HC (Head Circumference) — perimeter of the fetal head.
- TCD (Transcerebellar Diameter) — widest part of the fetal cerebellum.
- AC (Abdominal Circumference) — perimeter of the fetal abdomen.
- FL (Femur Length) — length of the fetal femur bone.
Action Items / Next Steps
- Practice the standardized 6-step and ISSUOG measurement approaches.
- Review scan images and key measurement landmarks.
- Complete any assigned readings on obstetric ultrasound protocols.