RDMS OB/GYN Exam Flashcards

Q: How many questions are on the RDMS OB/GYN exam?

The ARDMS OB/GYN specialty exam has 170 questions in 3 hours at Pearson VUE. The passing score is a scaled 555 on a 300–700 scale, approximately 70% correct.

Q: What is the largest domain on RDMS OB/GYN?

Second/Third Trimester Obstetrics is 37% of the exam—fetal biometry, anatomy survey, placental abnormalities, amniotic fluid, and biophysical profile are highest-yield topics.

Q: What are RDMS OB/GYN prerequisites?

Candidates must pass the SPI (Sonography Principles & Instrumentation) exam first and complete an ARDMS-eligible education or clinical experience pathway before scheduling the $275 specialty exam.

Q: How long should I study for RDMS OB/GYN?

Plan 150–250 hours over 8–12 weeks. Weight study time to Second/Third Trimester OB (37%) and Protocols & Procedures (24%)—together over 60% of scored content.

Question 1

Crown-Rump Length (CRL) Measurement Window

Accepted Answer

Most accurate for dating between 7 weeks 0 days and 13 weeks 6 days. Measured in a true sagittal plane with neutral fetal position; includes head and rump but excludes limbs.

Question 2

Intrauterine Gestational Sac (Early Pregnancy)

Accepted Answer

Seen transvaginally at ~5 weeks; should contain a yolk sac by ~5.5 weeks and fetal pole with cardiac activity by ~6 weeks. Absence of expected structures raises concern for failed pregnancy.

Question 3

Yolk Sac Significance

Accepted Answer

First sonographic evidence of intrauterine pregnancy. Abnormally large or irregular yolk sac correlates with increased risk of pregnancy loss. Should not be used alone for dating after CRL is measurable.

Question 4

Nuchal Translucency (NT) Screening

Accepted Answer

Measures fluid behind fetal neck at 11w0d–13w6d. Increased NT suggests aneuploidy and structural anomalies. Requires certified NT sonographers and calibrated equipment per FMF/AIUM standards.

Question 5

Ectopic Pregnancy Sonographic Clues

Accepted Answer

Adnexal mass separate from ovary, empty uterus, pseudogestational sac, or free fluid. Live ectopic with cardiac activity outside the uterus is diagnostic. Correlation with β-hCG and clinical findings is essential.

Question 6

Embryonic Demise Criteria

Accepted Answer

CRL ≥7 mm with no cardiac activity, or absence of cardiac activity ≥2 weeks after a gestational sac with yolk sac, or ≥11 days after a gestational sac without yolk sac—per accepted first-trimester guidelines.

Question 7

Biparietal Diameter (BPD)

Accepted Answer

Measured at the level of the thalami and cavum septi pellucidi, perpendicular to the falx. Used for biometry in the second and third trimesters; affected by head shape and breech presentation.

Question 8

Head Circumference (HC)

Accepted Answer

Measured around the outer skull table at the same thalamic plane as BPD. Combined with BPD, AC, and FL for composite gestational age and growth assessment.

Question 9

Abdominal Circumference (AC)

Accepted Answer

Measured at the skin line around the liver and umbilical vein at the portal sinus. Most sensitive single biometric for asymmetric fetal growth restriction.

Question 10

Femur Length (FL)

Accepted Answer

Measured from the greater trochanter to the distal metaphysis, excluding epiphyses. Short FL may suggest skeletal dysplasia, chromosomal abnormality, or asymmetric growth restriction.

Question 11

Estimated Fetal Weight (EFW) Percentiles

Accepted Answer

Derived from composite biometry formulas (e.g., Hadlock). <10th percentile suggests fetal growth restriction; >90th percentile suggests macrosomia. Single measurements are less reliable than composite EFW.

Question 12

Four-Chamber Fetal Heart View

Accepted Answer

Standard screening plane showing both atria, both ventricles, atrioventricular valves, and interventricular septum. Sits within the mid-trimester anatomic survey—major cardiac defects may be suspected here.

Question 13

Ventriculomegaly on OB Scan

Accepted Answer

Lateral ventricle atrium width ≥10 mm. Mild (10–12 mm) warrants follow-up; >15 mm suggests severe hydrocephalus. Measure at the glomus of the choroid plexus in the transthalamic plane.

Question 14

Spina Bifida Screening (Lemon & Banana Signs)

Accepted Answer

Lemon sign: frontal bone scalloping on axial cranium. Banana sign: cerebellum wrapped around brainstem in Chiari II malformation. Both are indirect markers of open neural tube defect.

Question 15

Placenta Previa vs. Low-Lying Placenta

Accepted Answer

Previa: placenta covers the internal cervical os. Low-lying: edge within 2 cm of os but not covering. Transvaginal sonography is the gold standard for cervical length and placental edge assessment.

Question 16

Placenta Accreta Spectrum

Accepted Answer

Abnormal trophoblast invasion into myometrium (accreta), into muscle (increta), or through serosa (percreta). Risk rises with prior cesarean and placenta previa. Look for loss of retroplacental clear space and bladder wall interruption.

Question 17

Single Deepest Pocket (SDP) Amniotic Fluid

Accepted Answer

Normal SDP 2–8 cm. <2 cm oligohydramnios; >8 cm may indicate polyhydramnios in a single-pocket assessment. Used when AFI is impractical (e.g., twins).

Question 18

Amniotic Fluid Index (AFI)

Accepted Answer

Sum of four quadrant vertical pockets. Normal ~8–24 cm (institution-specific). <5 cm oligohydramnios; >24 cm polyhydramnios. Assesses fetal urine production and membrane integrity.

Question 19

Biophysical Profile (BPP) Components

Accepted Answer

Five items (2 points each): fetal breathing, gross body movement, fetal tone, amniotic fluid volume, and NST (non-stress test). Score 8–10 is reassuring; ≤4 suggests delivery evaluation.

Question 20

Monochorionic Twin Complications

Accepted Answer

Single shared placenta risks twin-to-twin transfusion syndrome (TTTS), selective FGR, and twin anemia-polycythemia sequence (TAPS). Requires frequent surveillance with MCA Doppler and serial fluid assessment.

Question 21

Dichorionic Diamniotic Twins

Accepted Answer

Two placentas (or lambda/twin peak sign if fused), thick dividing membrane, and gender discordance confirms dichorionicity. Lower complication risk than monochorionic pairs.

Question 22

Umbilical Artery Doppler S/D Ratio

Accepted Answer

Elevated systolic/diastolic ratio and absent/reversed end-diastolic flow indicate increased placental resistance and fetal compromise. Used in growth restriction surveillance.

Question 23

Middle Cerebral Artery (MCA) Doppler

Accepted Answer

Brain-sparing reflex shows decreased MCA pulsatility index in fetal anemia or hypoxia. Peak systolic velocity >1.5 MoM suggests moderate–severe fetal anemia (e.g., alloimmunization).

Question 24

Uterine Artery Doppler (Preeclampsia Risk)

Accepted Answer

Notching and elevated PI after 24 weeks correlate with increased risk of preeclampsia and placental insufficiency. Often assessed during second-trimester aneuploidy/anatomy protocols.

Question 25

Normal Endometrium—Menstrual Phase

Accepted Answer

Thin echogenic line 1–4 mm during days 1–5 as the functionalis layer sloughs. Thick hyperechoic endometrium suggests secretory phase; trilaminar pattern indicates late proliferative/pre-ovulatory phase.

Question 26

Uterine Leiomyoma (Fibroid) Appearance

Accepted Answer

Well-defined hypoechoic or heterogeneous masses within or distorting the myometrium. Submucosal fibroids may impair fertility; calcified fibroids cast posterior acoustic shadowing.

Question 27

Adenomyosis Sonographic Features

Accepted Answer

Globular uterine enlargement, heterogeneous myometrium, myometrial cysts, and indistinct endometrial–myometrial junction. Often causes dysmenorrhea and menorrhagia.

Question 28

Simple Ovarian Cyst Criteria

Accepted Answer

Unilocular, anechoic, thin smooth wall, no solid components or internal vascularity. <3 cm in premenopausal women is usually physiologic; postmenopausal simple cysts need size/follow-up criteria per IOTA.

Question 29

Polycystic Ovary Morphology (Rotterdam)

Accepted Answer

≥20 follicles per ovary (2–9 mm) and/or ovarian volume >10 mL on adequate-frequency transducer. Requires clinical or biochemical hyperandrogenism for PCOS diagnosis—morphology alone is insufficient.

Question 30

Ovarian Torsion Ultrasound Findings

Accepted Answer

Enlarged ovary, peripheral follicles (string-of-pearls), decreased or absent arterial/venous flow on Doppler. Clinical pain and adnexal tenderness are key—Doppler cannot exclude torsion.

Question 31

Endometrial Thickness—Postmenopausal Bleeding

Accepted Answer

Endometrium ≤4 mm without bleeding has low malignancy risk; >4 mm or heterogeneous lining warrants further evaluation (biopsy/SIS). Hormone therapy alters thresholds.

Question 32

Broad Ligament Contents

Accepted Answer

Mesosalpinx, mesovarium, and mesometrium suspend the uterus, tubes, and ovaries. The uterine artery travels within the broad ligament—relevant for surgical and Doppler anatomy.

Question 33

Transvaginal vs. Transabdominal Pelvic Scan

Accepted Answer

TV offers superior resolution for early pregnancy, endometrium, and adnexa. TA requires full bladder for acoustic window and is preferred for large masses or late second-trimester overview.

Question 34

ALARA Principle in Obstetric Ultrasound

Accepted Answer

As Low As Reasonably Achievable—use lowest output settings and shortest scan time to obtain diagnostic information. Justify every scan and document medical indication.

Question 35

Thermal Index (TI) and Mechanical Index (MI)

Accepted Answer

TI estimates temperature rise potential; TIS for soft tissue, TIB for bone near focus. MI estimates cavitation risk. Keep indices as low as possible while maintaining diagnostic quality.

Question 36

AIUM/ACR Documentation Standards

Accepted Answer

Permanent images of all abnormal findings, biometry measurements, and survey structures. Reports must include indication, technique, comparison to prior, and impression with recommendations.

Question 37

Second-Trimester Anatomic Survey Timing

Accepted Answer

Typically 18–22 weeks. Systematic evaluation of fetal brain, spine, heart, abdomen, extremities, face, and placenta/cord. Incomplete views should be documented with follow-up plan.

Question 38

Fetal Lie, Presentation, and Position

Accepted Answer

Lie: long axis relative to maternal spine (longitudinal/oblique/transverse). Presentation: presenting part (cephalic/breech). Position: relationship of fetal back to maternal left or right.

Question 39

Color Doppler vs. Spectral Doppler

Accepted Answer

Color maps mean velocity and direction in a region. Spectral (pulsed-wave) displays velocity over time at a sample gate—required for PI, RI, and S/D calculations in fetal vessels.

Question 40

Patient Preparation for Pelvic Ultrasound

Accepted Answer

Endovaginal: empty bladder for best resolution. Transabdominal obstetric: moderately full bladder for early second trimester. Communicate prep instructions before the appointment.

Question 41

Acoustic Shadowing Artifact

Accepted Answer

Dark area distal to strongly attenuating structures (bone, calcification, gas). Helps identify stones, ribs, and calcified fibroids but can obscure posterior anatomy.

Question 42

Reverberation Artifact

Accepted Answer

Repeated bright parallel lines caused by sound bouncing between strong reflectors (e.g., needle, prosthetic valve). Can mimic extra structures if unrecognized.

Question 43

Axial Resolution vs. Lateral Resolution

Accepted Answer

Axial (along beam): improved by higher frequency and shorter pulse length. Lateral (across beam): improved by focused beam width and line density. Trade-off: higher frequency penetrates less.

Question 44

Doppler Angle Correction

Accepted Answer

Velocity measurements are accurate when the beam is ≤60° to flow direction (cosine correction). Angles >60° produce large error—align the sample volume parallel to vessel flow when possible.

Question 45

Harmonic Imaging Advantage

Accepted Answer

Uses returned harmonic frequencies to reduce near-field clutter and improve contrast resolution in difficult body habitus or late-gestation imaging.

Question 46

Placenta Grading (Manning Classification)

Accepted Answer

Grade 0 (smooth) to III (calcifications and basal indentations). Grading alone is a poor indicator of fetal maturity; clinical decisions rely more on biometry, fluid, and Doppler.

Question 47

Velamentous Cord Insertion

Accepted Answer

Umbilical vessels traverse membranes before reaching the placenta. Vasa previa risk if vessels cross the internal os—can rupture with membrane rupture causing fetal exsanguination.

Question 48

Rh Alloimmunization Surveillance

Accepted Answer

Sensitized pregnancies need serial MCA-PSV and possible cordocentesis. Rising MCA peak systolic velocity predicts fetal anemia before hydrops develops.

Question 49

IOTA Simple Rules (Adnexal Mass)

Accepted Answer

Benign features: unilocular, solid components <7 mm, smooth multilocular <10 cm. Malignant features: solid irregular mass, ascites, papillary projections with flow. Guides referral to gynecologic oncology.

Question 50

ARDMS RDMS OB/GYN Exam Format

Accepted Answer

170 questions in 3 hours at Pearson VUE. Passing scaled score 555 (~70%) on a 300–700 scale. Requires prior SPI credential and eligible clinical/education pathway. 60-day wait between retakes.

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