ARDMS Obstetrics and Gynecology (OB/GYN) Specialty Examination — Questions and Answers

Question 1: In twin pregnancies, what percentage of estimated fetal weight (EFW) discordance between twins is generally considered clinically significant?

Greater than 5%
Greater than 10%
Greater than 20% (Correct answer)
Greater than 30%

Correct answer: Greater than 20%

An EFW discordance exceeding 20% between twins is the widely accepted threshold for clinically significant growth discordance requiring closer surveillance.

Question 2: At what gestational age can chorionicity be most reliably determined by ultrasound?

6–7 weeks
11–14 weeks (Correct answer)
20–24 weeks anatomy scan
16–18 weeks

Correct answer: 11–14 weeks

The lambda and T-signs are most reliably identified between 11 and 14 weeks, making this the optimal window for chorionicity determination.

Question 3: What is typically assessed in the maternal ovaries during an ultrasound?

Hormone levels
Fetal development
The number of eggs
Presence of cysts or other abnormalities (Correct answer)

Correct answer: Presence of cysts or other abnormalities

While the primary focus of obstetric ultrasound is the fetus and uterus, the maternal ovaries are often visualized to check for any cysts, masses, or other abnormalities that could potentially complicate the pregnancy or require monitoring. This ensures a comprehensive assessment of the maternal pelvic organs.

Question 4: At what gestational age does the placenta normally migrate away from the cervical os?

After 36 weeks
At 20 weeks
At 16 weeks
By 28–32 weeks as the lower uterine segment develops (Correct answer)

Correct answer: By 28–32 weeks as the lower uterine segment develops

As the lower uterine segment elongates between 28 and 32 weeks, a low-lying placenta may appear to move away from the cervical os, a process called placental migration.

Question 5: Which layer of the uterus is responsible for its contraction during labor?

Decidua
Myometrium (Correct answer)
Perimetrium
Endometrium

Correct answer: Myometrium

The myometrium is the thick, muscular middle layer of the uterine wall. It is composed of smooth muscle fibers that are responsible for the powerful contractions during labor, which help to push the baby out of the uterus. The other layers have different functions, such as the endometrium lining the cavity and the perimetrium forming the outer covering.

Question 6: Serial ultrasound exams to monitor fetal growth are typically performed how far apart?

Daily
Every 6–8 weeks
Every 3–4 weeks (Correct answer)
Every week

Correct answer: Every 3–4 weeks

Serial growth scans are typically scheduled every 3 to 4 weeks, as shorter intervals do not allow enough time to detect meaningful growth changes.

Question 7: Why is the maternal uterus assessed during pregnancy ultrasounds?

To detect maternal infections
To monitor fetal development and placental health (Correct answer)
To measure maternal hormone levels
To evaluate pelvic bone structure

Correct answer: To monitor fetal development and placental health

The maternal uterus is the organ that houses and nourishes the developing fetus throughout pregnancy. Assessing it during ultrasound is crucial for monitoring fetal growth, position, and overall well-being, as well as evaluating the health and location of the placenta, which provides vital nutrients and oxygen to the baby.

Question 8: Which vessel is sampled in the ductus venosus Doppler assessment?

The main portal vein
The umbilical artery
The aorta
The fetal venous connection between the portal vein and inferior vena cava (Correct answer)

Correct answer: The fetal venous connection between the portal vein and inferior vena cava

The ductus venosus is a small venous shunt connecting the umbilical vein to the inferior vena cava, bypassing the fetal liver, and is sampled to assess cardiac preload.

Question 9: When is Doppler ultrasound considered safe to use in pregnancy?

Never before 20 weeks
Only in the third trimester
When indicated clinically, using the lowest output for the shortest time needed (Correct answer)
Only during non-stress tests

Correct answer: When indicated clinically, using the lowest output for the shortest time needed

Doppler ultrasound is safe when used for clinically indicated reasons following the ALARA principle, using minimum power output for the minimum time required.

Question 10: What is the cerebroplacental ratio (CPR) and why is it significant?

MCA PI plus UA PI
MCA velocity divided by UA velocity
UA PI divided by MCA PI
MCA PI divided by UA PI; low CPR indicates brain-sparing and fetal compromise (Correct answer)

Correct answer: MCA PI divided by UA PI; low CPR indicates brain-sparing and fetal compromise

The CPR is calculated as MCA PI divided by UA PI; a ratio below 1.0 indicates brain-sparing (redistribution) and is associated with adverse perinatal outcomes.

Question 11: What does an increased nuchal translucency (NT ≥3.5 mm) indicate?

Normal first-trimester finding
Confirms Down syndrome diagnosis
Increased risk of chromosomal abnormalities, cardiac defects, and genetic syndromes (Correct answer)
Only indicates Turner syndrome

Correct answer: Increased risk of chromosomal abnormalities, cardiac defects, and genetic syndromes

An NT of 3.5 mm or greater is associated with significantly increased risk of trisomies (21, 18, 13), Turner syndrome, cardiac defects, and various genetic syndromes.

Question 12: Why is transvaginal ultrasound preferred over transabdominal ultrasound in early first-trimester assessment?

It is safer for the fetus
It shows the whole uterus better
It provides higher resolution and can detect structures 1–2 weeks earlier than transabdominal scanning (Correct answer)
It is less uncomfortable

Correct answer: It provides higher resolution and can detect structures 1–2 weeks earlier than transabdominal scanning

Transvaginal ultrasound uses a higher frequency transducer placed closer to the uterus, providing superior resolution and detecting embryonic structures approximately 1 to 2 weeks earlier than transabdominal scanning.

Question 13: When measuring nuchal translucency (NT) in a twin pregnancy, how should the measurement be performed?

Add 2 mm to each twin's individual measurement as a twin correction factor
Only the larger twin's NT is measured to avoid redundancy
Each twin's NT is measured independently and compared to singleton reference ranges (Correct answer)
A single combined NT value is calculated for the pair

Correct answer: Each twin's NT is measured independently and compared to singleton reference ranges

Each twin's NT is measured independently using the same singleton reference ranges, as NT performance for aneuploidy screening has been validated using this approach.

Question 14: What is the role of the cervix during pregnancy?

It maintains pregnancy by remaining closed and shortens during labor. (Correct answer)
It supports fetal blood flow.
It facilitates the production of amniotic fluid.
It nourishes the fetus.

Correct answer: It maintains pregnancy by remaining closed and shortens during labor.

During pregnancy, the cervix plays a critical role in maintaining the pregnancy by remaining long and closed, forming a protective barrier for the fetus. As labor approaches, the cervix begins to soften, shorten (efface), and open (dilate) to allow the baby to pass through the birth canal. Its integrity is vital for preventing preterm birth.

Question 15: What is the earliest structure visualized on transvaginal ultrasound in a normal intrauterine pregnancy?

Fetal pole
Yolk sac
Fetal heartbeat
Gestational sac (Correct answer)

Correct answer: Gestational sac

The gestational sac is the earliest structure visible on transvaginal ultrasound, typically seen by 4.5 to 5 weeks of gestation as a small anechoic structure within the decidua.

Question 16: At what atrial width measurement is ventriculomegaly diagnosed?

Greater than 10 mm (Correct answer)
Greater than 8 mm
Greater than 15 mm
Greater than 12 mm

Correct answer: Greater than 10 mm

Ventriculomegaly is diagnosed when the atrium of the lateral ventricle measures greater than 10 mm; measurements between 10–15 mm are mild and above 15 mm are severe.

Question 17: Which ultrasound finding best distinguishes dichorionic-diamniotic (DCDA) twins from monochorionic-diamniotic (MCDA) twins in the first trimester?

Twin peak (lambda) sign at placental insertion (Correct answer)
Number of yolk sacs visible
Presence of any dividing membrane
Crown-rump length discordance greater than 5 days

Correct answer: Twin peak (lambda) sign at placental insertion

The lambda (twin peak) sign represents chorionic villi extending into the base of the inter-twin membrane, indicating dichorionic placentation.

Question 18: At what beta-hCG level should a gestational sac be visible on transvaginal ultrasound?

5,000 mIU/mL
500 mIU/mL
10,000 mIU/mL
1,500–2,000 mIU/mL (Correct answer)

Correct answer: 1,500–2,000 mIU/mL

A gestational sac should be visible on transvaginal ultrasound when serum beta-hCG reaches approximately 1,500 to 2,000 mIU/mL; failure to visualize raises concern for ectopic pregnancy.

Question 19: How is the maternal bladder relevant during an early pregnancy ultrasound?

It stores hormones for the fetus.
It provides nutrients to the uterus.
It is used to measure fetal urine output.
A full bladder helps improve visualization of pelvic structures. (Correct answer)

Correct answer: A full bladder helps improve visualization of pelvic structures.

In early pregnancy, especially during transabdominal ultrasounds, a full maternal bladder is often required. The fluid-filled bladder acts as an acoustic window, pushing the uterus and other pelvic structures into a more favorable position and improving the transmission of sound waves, which enhances the visualization of the early gestational sac and embryo.

Question 20: A hyperechoic bowel finding on second-trimester ultrasound may indicate which condition?

Gastroschisis
Cystic fibrosis, Down syndrome, or cytomegalovirus infection (Correct answer)
Duodenal atresia
Normal variant only

Correct answer: Cystic fibrosis, Down syndrome, or cytomegalovirus infection

Echogenic bowel (bowel as bright as bone) is a soft marker associated with cystic fibrosis, Down syndrome, CMV infection, and fetal swallowing of blood.

Question 21: What is an omphalocele?

A bladder exstrophy
A right-sided defect with free bowel herniation
A midline abdominal wall defect with herniation of organs covered by a membrane (Correct answer)
A diaphragmatic hernia

Correct answer: A midline abdominal wall defect with herniation of organs covered by a membrane

An omphalocele is a midline defect at the umbilical cord insertion where abdominal organs herniate into the base of the cord, covered by a peritoneal/amniotic membrane.

Question 22: What does IUGR stand for in obstetric ultrasound?

Intrauterine Growth Restriction (Correct answer)
Intrauterine Gestational Ratio
Internal Uterine Growth Rate
Integrated Uterine Growth Response

Correct answer: Intrauterine Growth Restriction

IUGR (Intrauterine Growth Restriction) refers to a condition where the fetus does not grow at the expected rate inside the womb.

Question 23: Which ultrasound finding is associated with placenta accreta spectrum?

Loss of the retroplacental hypoechoic zone (Correct answer)
Bilobed placenta
Thick placenta over 5 cm
Placenta in the fundus

Correct answer: Loss of the retroplacental hypoechoic zone

Loss of the normal retroplacental hypoechoic (clear) zone between the placenta and myometrium is a key ultrasound sign of placenta accreta.

Question 24: What is the significance of bilateral renal pyelectasis on a second-trimester scan?

It requires immediate delivery
It confirms vesicoureteral reflux
It always indicates severe obstruction
It is a soft marker for Down syndrome and warrants follow-up (Correct answer)

Correct answer: It is a soft marker for Down syndrome and warrants follow-up

Bilateral renal pyelectasis (mild pelviectasis ≥4 mm AP) is a soft marker for Down syndrome and warrants follow-up to assess for persistent hydronephrosis.

Question 25: What color Doppler setting adjustment is most important for detecting low-velocity venous flow?

Increasing the transducer frequency
Lowering the color velocity scale (PRF) (Correct answer)
Decreasing the depth
Increasing the PRF

Correct answer: Lowering the color velocity scale (PRF)

Lowering the pulse repetition frequency (PRF/color scale) is essential for visualizing low-velocity venous flow, as too high a scale will not display slow-moving blood.

Question 26: What ultrasound finding definitively differentiates monochorionic-monoamniotic (MCMA) twins from monochorionic-diamniotic (MCDA) twins?

Complete absence of any dividing membrane between the twins (Correct answer)
Differing cord insertion sites on the placenta
Presence of the T-sign versus no T-sign
Lambda sign present versus absent

Correct answer: Complete absence of any dividing membrane between the twins

The complete absence of a dividing membrane confirms MCMA twinning, whereas MCDA twins have a thin but identifiable membrane separating their sacs.

Question 27: What is macrosomia defined as in ultrasound practice?

Estimated fetal weight above the 75th percentile
Estimated fetal weight above the 90th percentile (Correct answer)
Femur length above normal limits
Birth weight over 3,000 grams

Correct answer: Estimated fetal weight above the 90th percentile

Macrosomia is defined as an estimated fetal weight above the 90th percentile for gestational age, or commonly above 4,000–4,500 grams at term.

Question 28: What is a subchorionic hemorrhage (SCH) on first-trimester ultrasound?

Blood within the gestational sac
Placental abruption
Hemorrhage within the embryo
A collection of blood between the gestational sac and the uterine wall (Correct answer)

Correct answer: A collection of blood between the gestational sac and the uterine wall

An SCH is a crescent-shaped collection of blood between the chorionic membrane of the gestational sac and the uterine wall, associated with an increased risk of miscarriage.

Question 29: Which ultrasound finding is most characteristic and pathognomonic of monochorionic-monoamniotic (MCMA) twins?

Umbilical cord entanglement between the twins (Correct answer)
Thin dividing membrane measuring less than 2 mm
Significant estimated fetal weight discordance
Lambda sign at placental insertion

Correct answer: Umbilical cord entanglement between the twins

Cord entanglement is pathognomonic for MCMA twins because both fetuses share a single amniotic cavity with no membrane separating their cords.

ARDMS Obstetrics and Gynecology (OB/GYN) Specialty Examination

The ARDMS OB/GYN specialty examination certifies diagnostic medical sonographers in obstetric and gynecologic ultrasound, covering pelvic anatomy, first and second/third trimester obstetrics, ultrasound protocols and procedures, and physics instrumentation.

Questions

35 min

Time Limit

70%

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