Obstetrics & Gynecology (OB/GYN) Specialty Exam Prep

The ARDMS OB/GYN specialty exam has the highest first-time pass rate among all seven specialties (80% in 2025), but its content breadth is substantial. It covers the full spectrum of obstetric and gynecologic ultrasound: normal and abnormal pregnancy, fetal anatomy survey, biometry, Doppler surveillance, and gynecologic pathology.

What the OB/GYN Exam Covers

The Obstetrics & Gynecology registration is a 170-question, 3-hour examination administered by the ARDMS. Work through every content domain in proportion to its published weight rather than reviewing only familiar topics.

Who This Exam Is For

The OB/GYN credential suits both sonography students sitting for their first registration and practicing sonographers adding a new specialty. The outline covers material that may not come up in every clinical setting. Mapping each study block to a specific domain helps you review the published scope.

Exam Facts

Credential earned: RDMS
Exam format: 170-question, 3-hour examination
Passing score: 555/700

2025 Pass Rates

First-time candidates: 80%; repeat candidates: 50%; overall: 75%. This 30-percentage-point difference compares separate candidate groups; it does not measure changes in exam difficulty or the effectiveness of a study strategy.

For repeat candidates, the 2024 report listed 57% versus 50% in 2025. These are different groups; the reports do not explain the change.

Source: ARDMS/APCA Global Exam Performance Summary Report, 2025; 2024 report for the comparison.

High-Yield Focus Areas

First trimester dating and viability assessment
Fetal biometry and growth assessment
Placental evaluation and complications
Gynecologic pathology identification
Ectopic pregnancy and early pregnancy complications

Common Mistakes to Avoid

Using incorrect dating parameters for gestational age
Misidentifying placenta previa vs. low-lying placenta
Confusing endometrioma with hemorrhagic cyst
Incorrectly measuring amniotic fluid index
Missing the signs of ectopic pregnancy in early scans

Study Tips

Create a timeline chart of normal embryologic development by gestational week
Master the biometry measurements: BPD, HC, AC, and FL with their appropriate gestational ages
Study gynecologic pathology by organ: uterine, ovarian, and adnexal
Review ectopic pregnancy locations and their sonographic appearances
Practice calculating estimated fetal weight and understanding growth percentiles

Sample Question Types

Illustrative prompts, not actual registry questions.

At what gestational age should the yolk sac be visible on transvaginal ultrasound?
Which biometric measurement is least affected by fetal position?
What is the most common location for an ectopic pregnancy?
A complex adnexal mass with internal echoes and no blood flow is most consistent with what?

Key Topics

First trimester assessment
Fetal biometry
Placental evaluation
Amniotic fluid assessment
Ectopic pregnancy
Uterine pathology
Ovarian pathology
Cervical assessment
Multiple gestation
Fetal anatomy survey
Growth restriction
Gynecologic imaging

How to Prepare

Take specialty quizzes or a timed exam and review missed concepts using domain-level analytics. Platform question-bank inventory and mock exams are separate from official exam-format facts.

Related Specialties & Resources

Explore these related specialties when planning another registration:

Browse the seven ARDMS specialties we cover, weigh your options on the specialty comparison hub, or read study guides on the Ultrasound Analytics blog.