This ARDMS OB/GYN last-minute review gathers the measurements, cut-offs and classic signs that the OB/GYN registry loves to test, from early pregnancy to fetal anomalies and gynaecology.
| OB/GYN exam at a glance | |
|---|---|
| Questions | About 170, including hotspot questions |
| Time | 3 hours |
| Fee | US$300 |
| Passing score | 555 on a 300–700 scale |
| Content areas | Gynaecology (pelvic anatomy and physiology), first to third trimester obstetrics, protocols and procedures, and physics and instrumentation |
A 7-day final plan
| Day | Focus |
|---|---|
| 7 | Gynaecology: uterus, endometrium, ovaries, adnexal masses and the menstrual cycle |
| 6 | First trimester: normal early pregnancy, failure criteria and ectopic pregnancy |
| 5 | Fetal anatomy survey: brain, spine, face, heart, abdomen and limbs |
| 4 | Placenta, cord, amniotic fluid, multiples and fetal growth |
| 3 | Fetal anomalies, aneuploidy markers and Doppler |
| 2 | Full timed mock (170 questions in 3 hours) and review |
| 1 | Numbers table and rest |
Numbers to memorise
| Measurement | Key value |
|---|---|
| Pregnancy failure (definitive) | Crown–rump length 7 mm or more with no heartbeat, or mean sac diameter 25 mm or more with no embryo |
| Nuchal translucency | Measured at 11–14 weeks; 3.0–3.5 mm or more is increased |
| Nuchal fold (second trimester) | 6 mm or more is abnormal |
| Lateral ventricle atrium | 10 mm or more means ventriculomegaly |
| Cisterna magna | About 2–10 mm |
| Amniotic fluid | AFI about 5–24 cm; deepest pocket 2–8 cm |
| Cervical length | Under 25 mm before 24 weeks is short |
| Placenta to internal os | Under 2 cm is low-lying; covering the os is previa (reassess in the third trimester) |
| Postmenopausal endometrium with bleeding | 4 mm or less is reassuring |
| Simple ovarian cyst (premenopausal) | Up to 3 cm is usually a normal follicle |
Classic signs
| Sign | Means |
|---|---|
| Lemon and banana signs | Open spina bifida with Chiari II |
| Double bubble | Duodenal atresia (associated with trisomy 21) |
| Lambda (twin peak) sign | Dichorionic twins |
| T sign | Monochorionic diamniotic twins |
| Ring of fire on colour Doppler | Corpus luteum or ectopic pregnancy |
| Snowstorm appearance, no fetus | Complete molar pregnancy |
| String of pearls ovary | Polycystic ovarian morphology |
| Ground-glass cyst | Endometrioma |
| Echogenic bowel, short femur, cardiac echogenic focus | Soft markers for aneuploidy |
| Absent or reversed umbilical artery end-diastolic flow | Placental insufficiency, high risk |
Early pregnancy and ectopic in a nutshell
- The yolk sac is the first structure that confirms an intrauterine pregnancy.
- An empty uterus with a raised β-hCG and an adnexal mass separate from the ovary suggests ectopic pregnancy; free fluid with echoes suggests haemorrhage.
- An interstitial (cornual) ectopic shows an eccentric sac with a thin myometrial mantle.
1,000 OB/GYN practice questions
The ARDMS Q Bank has 1,000 explained OB/GYN questions, plus SPI, Abdomen, Vascular, MSK and Breast pools, in tutor or timed mode.
Open the ARDMS Q BankThe day before and exam day
- Stop new topics 24 hours before. Skim your own notes and the tables on this page, then rest.
- Check your Pearson VUE confirmation: test centre address, start time and the exact name on your ID, which must match your registration.
- Arrive 30 minutes early with your valid, government-issued photo ID.
- Use the flag button: answer every question on the first pass, flag the slow ones, then come back. There is no penalty for guessing, so never leave a blank.
- Hotspot questions: read exactly what is asked, then click precisely on the structure or finding.
- If you don't pass: you can reapply after 3 days but must wait 60 days to re-sit, so plan a focused 8-week review of your weak domains.
Frequently asked questions
How many questions are on the ARDMS OB/GYN exam?
About 170 questions in 3 hours, including multiple-choice and hotspot questions.
What is the passing score for the OB/GYN registry?
555 on a 300–700 scale. It is not a percentage.
What are the highest-yield OB/GYN topics?
Early pregnancy and failure criteria, ectopic pregnancy, the fetal anatomy survey, neural tube and cardiac anomalies, placenta and cord, multiple pregnancy, and gynaecological masses.
What are the criteria for a failed pregnancy on ultrasound?
A crown–rump length of 7 mm or more without a heartbeat, or a mean sac diameter of 25 mm or more without an embryo, are definitive for pregnancy failure.
Do I need SPI for the OB/GYN credential?
Yes. To earn RDMS with OB/GYN, you must pass SPI and the OB/GYN specialty within five years of each other, in either order.
Exam facts from Inteleos (ARDMS) exam pages, checked October 2026. Always confirm current rules on inteleos.org. Radiology Boards is not affiliated with ARDMS or Inteleos.