PU First Trimester Ultrasound and Dating 2 — Questions and Answers
Question 1: What finding on first-trimester ultrasound is most suggestive of a failed pregnancy (missed abortion)?
- CRL ≥7 mm with no cardiac activity on transvaginal scan (Correct answer)
- Small gestational sac
- Single umbilical artery
- Anterior placenta
Correct answer: CRL ≥7 mm with no cardiac activity on transvaginal scan
Per ACOG/SRU criteria, a CRL of 7 mm or greater with no visible cardiac activity on transvaginal ultrasound is diagnostic of embryonic demise.
Question 2: What is the normal fetal heart rate range in the first trimester?
- 100–170 bpm (Correct answer)
- 60–80 bpm
- 180–220 bpm
- 50–60 bpm
Correct answer: 100–170 bpm
Normal first-trimester fetal heart rates range from approximately 100 to 170 beats per minute, with rates below 100 bpm at 6–8 weeks associated with poor prognosis.
Question 3: What is the mean sac diameter (MSD)?
- The average of three perpendicular measurements of the gestational sac (Correct answer)
- The length of the sac only
- The width of the sac only
- The sac measurement minus the yolk sac
Correct answer: The average of three perpendicular measurements of the gestational sac
MSD is calculated by averaging three perpendicular internal measurements (length, width, height) of the gestational sac and is used to assess early pregnancy development.
Question 4: The nuchal translucency (NT) measurement is performed at what gestational age range?
- 11–14 weeks (CRL 45–84 mm) (Correct answer)
- 8–10 weeks
- 15–20 weeks
- 6–8 weeks
Correct answer: 11–14 weeks (CRL 45–84 mm)
NT measurement is performed between 11+0 and 13+6 weeks gestation, when the CRL is between 45 and 84 mm, for first-trimester Down syndrome screening.
Question 5: What does an increased nuchal translucency (NT ≥3.5 mm) indicate?
- Increased risk of chromosomal abnormalities, cardiac defects, and genetic syndromes (Correct answer)
- Normal first-trimester finding
- Confirms Down syndrome diagnosis
- 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 6: What structure should always be visualized within a gestational sac before a CRL is measurable?
- Yolk sac (Correct answer)
- Amnion
- Fetal pole
- Umbilical cord
Correct answer: Yolk sac
The yolk sac must be visible within the gestational sac before an embryo/CRL is measurable and confirms the sac is a true gestational sac rather than a pseudosac.
PU First Trimester Ultrasound and Dating 2
What finding on first-trimester ultrasound is most suggestive of a failed pregnancy (missed abortion)?