ARDMS OB/GYN Exam: The Complete Guide (2026)
Last Updated: January 2026 | Reading Time: 20 minutes
Quick Summary: The ARDMS OB/GYN (Obstetrics and Gynecology) specialty exam is a 170-question, 3-hour test that validates your expertise in fetal, obstetric, and gynecologic sonography. This comprehensive guide covers the exam format, all five content domains, 10 free practice questions, registration steps, and proven study strategies to help you earn your RDMS credential.
Table of Contents
What is the OB/GYN Exam?
Why the OB/GYN is Challenging
The OB/GYN is often considered one of the more challenging exams because:
- Extensive anatomy knowledge: You must understand normal and abnormal fetal development across all three trimesters, plus female pelvic anatomy
- Critical measurements: Biometric measurements (BPD, HC, AC, FL) and their gestational age correlations must be precise
- High-stakes diagnoses: Identifying fetal anomalies, placental abnormalities, and gynecologic pathology requires thorough preparation
- Broad scope: The exam covers obstetrics, gynecology, protocols, and physics across five content domains
OB/GYN Exam Format & Structure
Understanding the exam format helps you prepare strategically:
| Aspect | Details |
|---|---|
| Total Questions | Approximately 165 multiple-choice |
| Time Limit | 3 hours (180 minutes) |
| Passing Score | 555 (on a 300-700 scale) |
| Format | Multiple choice and hotspot questions with ultrasound images |
| Testing Centers | Pearson VUE (in-person or online proctoring) |
| Exam Fee | $300 (as of 2026) |
Understanding the 5 Content Domains
The OB/GYN exam is divided into 5 content domains, each weighted differently. Knowing these weights helps you prioritize your study time.
Content Domain Weights
Question estimates based on total question count. Focus study time proportionally.
Study tip: Spend the most time on the largest domain—it makes up the biggest portion of your exam.
Domain 1: Gynecology - Pelvic Anatomy and Physiology (19%)
Approximately 31 questions
Domain 2: Obstetrics - First Trimester (12%)
Approximately 20 questions
Domain 3: Obstetrics - Second/Third Trimester (37%)
Approximately 61 questions
Domain 4: Protocols and Procedures (24%)
Approximately 40 questions
Domain 5: Physics and Instrumentation (8%)
Approximately 13 questions
Crown-rump length (CRL): Most accurate first trimester dating (6-13 weeks)
Biparietal diameter (BPD): Outer edge to inner edge of skull
Head circumference (HC): Measured at level of thalami and cavum septi pellucidi
Abdominal circumference (AC): At level of umbilical vein/portal sinus
Femur length (FL): Ossified diaphysis only
Estimated fetal weight (EFW): Derived from BPD, HC, AC, and FL
Amniotic fluid index (AFI): Sum of four quadrant measurements
Single deepest pocket (SDP): Alternative to AFI
Nuchal translucency (NT): Measured 11-14 weeks, CRL 45-84mm
Free OB/GYN Practice Test Questions
Test your knowledge with these sample OB/GYN exam questions. Answers and explanations are provided below.
Question 1
Which measurement is most accurate for establishing gestational age in the first trimester?
Question 2
What is the normal range for amniotic fluid index (AFI) in the second and third trimesters?
Question 3
A complete placenta previa is defined as:
Question 4
At what gestational age should the fetal heartbeat be visualized with transvaginal ultrasound?
Question 5
Which finding is most suggestive of an ectopic pregnancy?
Question 6
What is the most common location for uterine fibroids (leiomyomas)?
Question 7
The nuchal translucency measurement should be obtained between:
Question 8
Which structure should NOT be visualized in the normal four-chamber heart view?
Question 9
What sonographic appearance is characteristic of a dermoid cyst (mature cystic teratoma)?
Question 10
In a biophysical profile (BPP), which parameter is NOT assessed?
Answer Key with Explanations
Crown-rump length (CRL) is the most accurate measurement for establishing gestational age in the first trimester (6-13 weeks), with an accuracy of +/- 3-5 days. After 14 weeks, multiple biometric parameters are used.
Normal AFI ranges from 5-25 cm. Less than 5 cm indicates oligohydramnios, while greater than 25 cm indicates polyhydramnios. Single deepest pocket less than 2 cm or greater than 8 cm are alternative criteria.
Complete placenta previa occurs when the placenta completely covers the internal cervical os. Marginal previa is within 2 cm of the os, and low-lying placenta is within 2-3.5 cm but not covering it.
Fetal cardiac activity should be visible by transvaginal ultrasound when the embryo reaches 5-6 mm in length, typically around 6-6.5 weeks gestational age. A yolk sac is usually seen by 5.5 weeks.
The 'ring of fire' sign refers to increased peripheral vascularity around an adnexal mass on color Doppler, which is highly suggestive of ectopic pregnancy. An intrauterine gestational sac with yolk sac confirms intrauterine pregnancy.
Intramural fibroids, located within the myometrium, are the most common type (55-65%). Subserosal fibroids project from the outer uterine surface, while submucosal fibroids project into the uterine cavity.
Nuchal translucency (NT) is measured between 11 weeks 0 days and 13 weeks 6 days, when CRL is between 45-84 mm. Increased NT (>3 mm) is associated with chromosomal abnormalities and structural defects.
A ventricular septal defect (VSD) is an abnormal finding. The normal four-chamber view should show both ventricles, both atria, the interventricular septum, and the foramen ovale (a normal fetal structure).
Dermoid cysts typically appear as complex masses with echogenic components (fat, hair, teeth) that may cause acoustic shadowing. The 'tip of the iceberg' sign occurs when only the near-field echogenic portion is visible.
The five parameters of BPP are: fetal breathing movements, gross body movement, fetal tone, amniotic fluid volume, and non-stress test (fetal heart rate reactivity). Placental grading is not part of the BPP scoring system.
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OB/GYN Exam Scoring & Pass Rate
Current Pass Rates
According to official data, the OB/GYN first-time pass rate is approximately 73%. This makes it one of the more challenging exams.
Why Pass Rates May Be Lower
- Volume of material: Covers entire gestational development plus comprehensive gynecologic pathology
- Measurement precision: Must know exact landmarks and techniques for all biometric measurements
- Pattern recognition: Identifying subtle anomalies requires extensive image review
- Clinical correlation: Understanding how findings impact patient management
Understanding Your Score Report
Your score report includes:
- Overall scaled score (pass/fail)
- Performance breakdown by content domain
- Percentile ranking compared to other examinees
What If You Don't Pass?
First, know that you're not alone—many examinees don't pass on their first attempt.
- Waiting period: 60 days before you can retake
- Maximum attempts: 3 attempts per 12-month period
- Re-application: You must submit a new application and fee for each attempt
How to Register for the OB/GYN Exam
Step 1: Ensure SPI Completion or Concurrent Registration
To earn your RDMS credential, you must pass both the SPI exam and this specialty exam. You can register for both simultaneously or complete SPI first.
Step 2: Create an ARDMS Account
Visit myARDMS.org, create a new account or log in, and complete your profile information.
Step 3: Verify Your Eligibility
ARDMS offers several pathways to OB/GYN exam eligibility:
- Pathway 1: Graduate from a CAAHEP-accredited sonography program with OB/GYN clinical training
- Pathway 2: Currently enrolled in final semester of accredited program
- Pathway 3: Hold appropriate prerequisite credentials with documented OB/GYN experience
- Pathway 4: Documented clinical OB/GYN sonography work experience
Step 4: Submit Your Application
Select 'OB/GYN Examination' from available specialty exams, choose your eligibility pathway, upload required documentation, and pay the application fee ($275 as of 2026).
Step 5: Receive Your Authorization to Test (ATT)
ARDMS reviews applications within 2-4 weeks. Upon approval, you'll receive an ATT via email. Your ATT is valid for 90 days.
Step 6: Schedule with Pearson VUE
Visit Pearson VUE, choose in-person or online proctoring, select your preferred date and time, and confirm your appointment.
What to Expect on Exam Day
For In-Person Testing
Before arrival:
- Get 7-8 hours of sleep
- Eat a balanced meal (3-hour exam requires sustained energy)
- Arrive 30 minutes early
- Bring two forms of valid ID (one with photo and signature)
At the testing center:
- Check in with the test administrator
- Store personal belongings in a locker (no phones, watches, or notes)
- Palm vein scan or photo may be taken for security
During the exam:
- You'll have 180 minutes for 170 questions (~63 seconds per question)
- Breaks are permitted but count against your time
- Flag difficult questions and return to them
- Raise your hand if you need administrator assistance
For Online Proctoring
System requirements:
- Reliable high-speed internet
- Webcam and microphone
- Windows or Mac computer (no tablets)
- Quiet, private room for 3+ hours
Environment requirements:
- Clear desk (remove all items except computer)
- No dual monitors
- Well-lit room
- No interruptions for the full exam duration
How Long Should You Study?
The ideal study timeline depends on your background:
| Situation | Recommended Study Time |
|---|---|
| Currently in school (OB/GYN rotation) | 6-8 weeks |
| Recent graduate (< 1 year) | 8-10 weeks |
| Working sonographer (1-3 years OB/GYN experience) | 6-8 weeks |
| Crossing over from another specialty | 10-14 weeks |
Sample Study Schedule
Week 1-2: Gynecology Foundation
- Review normal pelvic anatomy (uterus, ovaries, fallopian tubes)
- Study Domain 1: Pelvic anatomy and physiology (19%)
- Learn common gynecologic pathology (fibroids, cysts, endometriosis)
- Complete 100-150 practice questions
Complete 100-150 practice questions
Week 3-4: First Trimester Obstetrics
- Study Domain 2: First Trimester (12%)
- Master early pregnancy assessment (yolk sac, CRL, cardiac activity)
- Learn ectopic pregnancy findings and locations
- Understand first trimester screening (NT, biochemical markers)
Complete 150-200 practice questions
Week 5-6: Second/Third Trimester (Critical)
- Dedicate significant time to Domain 3 (37% of exam)
- Master all biometric measurements (BPD, HC, AC, FL)
- Study fetal anatomy survey and anomaly detection
- Learn placental evaluation, amniotic fluid assessment, BPP
Complete 200-250 practice questions
Week 7: Protocols, Procedures & Physics
- Study Domain 4: Protocols and Procedures (24%)
- Review Domain 5: Physics and Instrumentation (8%)
- Understand documentation requirements and patient care
- Take first full-length mock exam
Complete 200 practice questions
Week 8: Final Preparation
- Take 2-3 timed mock exams (170 questions in 3 hours)
- Review all missed questions and weak areas
- Focus on image recognition and case-based questions
- Rest the day before your exam
Free Video Lessons
Free Video Lessons
Watch these free video lessons to help you prepare for the OB/GYN.
Tips to Pass the OB/GYN Exam
1. Master the Measurements
Know exactly where to place calipers for every biometric measurement. BPD at the thalami, AC at the umbilical vein/portal sinus, FL on ossified diaphysis only. Incorrect technique questions are common.
2. Focus on Second/Third Trimester
This domain accounts for 37% of the exam. Spend proportionally more time on fetal anatomy, anomaly detection, and growth assessment. Know the normal appearance of every fetal structure.
3. Learn the Red Flags
Know findings that require immediate action: absent cardiac activity, placental abruption signs, cord prolapse, severe oligohydramnios. Understanding clinical urgency helps with protocol questions.
4. Review Real Cases
The exam includes many image-based questions. Review as many normal and abnormal ultrasound images as possible. Pattern recognition improves with exposure.
5. Understand Normal Variants
Know what's normal at each gestational age. Physiologic bowel herniation at 8-11 weeks is normal; after 12 weeks it's abnormal. Context matters for every finding.
6. Pace Yourself
With 170 questions in 180 minutes, you have about 63 seconds per question. Flag difficult questions and return to them. Don't spend 5 minutes on one question at the expense of others.
FAQs
How many questions are on the OB/GYN exam?
The OB/GYN exam contains approximately 165 multiple-choice questions.
What is the passing score for the OB/GYN exam?
You need a scaled score of 555 or higher (on a 300-700 scale) to pass.
How long is the OB/GYN exam?
You have 3 hours (180 minutes) to complete the exam, giving you approximately 63 seconds per question.
What is the OB/GYN exam pass rate?
The current first-time pass rate is approximately 73%.
How much does the OB/GYN exam cost?
The examination fee is $275 (as of 2026).
Do I need to pass the SPI before taking the OB/GYN exam?
No, you can take the exams in either order or register for both simultaneously. However, you must pass both to earn your RDMS credential.
How many times can I take the OB/GYN exam?
You can attempt the exam up to 3 times within a 12-month period with a mandatory 60-day waiting period between attempts.
What content areas are covered on the OB/GYN exam?
The exam covers five domains: Gynecology - Pelvic Anatomy and Physiology (19%), First Trimester Obstetrics (12%), Second/Third Trimester Obstetrics (37%), Protocols and Procedures (24%), and Physics and Instrumentation (8%).
How do I know if I'm ready for the OB/GYN exam?
Aim for 80-85% accuracy on practice exams under timed conditions before scheduling your test, with consistent performance across all five domains.
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This guide is updated regularly to reflect the latest ARDMS OB/GYN exam information. Last reviewed: January 2026.