RDMS OB/GYN study guide
RDMS OB/GYN · Work through your exam, one topic at a time.
The Registered Diagnostic Medical Sonographer (RDMS) credential with an Obstetrics and Gynecology specialty is the ARDMS pathway for sonographers whose practice centers on pregnancy imaging and on gynecologic ultrasound of the uterus, ovaries, and adnexa. ARDMS is a member community of Inteleos, and its certifications are built around career-long learning, verified proficiency, and patient safety. The RDMS OB/GYN study guide has 5 sections and about 1,684 words.
01First Trimester Obstetric Sonography: Normal and Abnormal
Transvaginal scanning shows a gestational sac at about 4.5–5 weeks (mean sac diameter 2–3 mm), a yolk sac once the MSD reaches 8 mm, and an embryo with cardiac activity by 5.5–6 weeks. Confirm intrauterine location with the intradecidual sign and double decidual sac sign, and document adnexa bilaterally.
356 words, about 2 min02Second and Third Trimester Fetal Anatomy, Biometry, and Anomalies
Biparietal diameter and head circumference use an axial plane at the level of the thalami and cavum septi pellucidi, with a thin symmetric calvarial rim and the falx interrupted anteriorly. Abdominal circumference is measured where the stomach bubble and portal sinus/umbilical vein are seen, on a circular section with symmetric ribs.
330 words, about 2 min03Pregnancy Complications and Fetal Well-Being: Placenta, Fluid, Twins, Growth
Placenta previa is placental tissue covering the internal os; low-lying placenta lies near but not over it, and most apparent low-lying placentas at the 18–22 week scan resolve by term as the lower segment forms. Placenta accreta spectrum is suggested by previa with prior cesarean, placental lacunae, loss of the clear zone, and bladder wall irregularity.
344 words, about 2 min04Gynecologic Sonography: Uterus, Ovaries, and Adnexa
Measure the uterus in sagittal and transverse planes and describe version, flexion, and contour. Endometrial thickness is the maximal anteroposterior double-layer measurement in a true sagittal plane.
306 words, about 2 min05Instrumentation, Technique, Artifacts, and Interventional Procedures
Choose the highest-frequency transducer that still provides adequate penetration: 5–9 MHz transvaginal for pelvic detail, 3.5–5 MHz transabdominal for larger or deeper structures. The focal zone belongs at the level of interest, and overall gain and time-gain compensation should be adjusted so fluid is anechoic without losing far-field detail.
348 words, about 2 min