PU First Trimester Ultrasound and Dating 1 — Questions and Answers
Question 1: What is the earliest structure visualized on transvaginal ultrasound in a normal intrauterine pregnancy?
- Gestational sac (Correct answer)
- Yolk sac
- Fetal pole
- Fetal heartbeat
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 2: At what beta-hCG level should a gestational sac be visible on transvaginal ultrasound?
- 1,500–2,000 mIU/mL (Correct answer)
- 500 mIU/mL
- 5,000 mIU/mL
- 10,000 mIU/mL
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 3: What is the normal location for a yolk sac in early pregnancy?
- Within the gestational sac between the amnion and chorion (Correct answer)
- Inside the embryo
- Outside the gestational sac
- Adjacent to the decidua
Correct answer: Within the gestational sac between the amnion and chorion
The yolk sac is located within the gestational sac in the chorionic space (between the amnion and chorion) and is the first structure seen inside the sac before the embryo.
Question 4: What is the double decidual sac sign (DDSS)?
- Two concentric rings of decidua surrounding the gestational sac, confirming intrauterine location (Correct answer)
- A twin pregnancy
- A sign of ectopic pregnancy
- The appearance of a bicornuate uterus
Correct answer: Two concentric rings of decidua surrounding the gestational sac, confirming intrauterine location
The DDSS describes two concentric echogenic rings surrounding the gestational sac — the decidua capsularis and decidua parietalis — confirming intrauterine implantation.
Question 5: What crown-rump length (CRL) corresponds to the first detectable fetal cardiac activity?
- 2–4 mm (approximately 5.5–6 weeks) (Correct answer)
- 8–10 mm
- 15 mm
- 1 mm
Correct answer: 2–4 mm (approximately 5.5–6 weeks)
Fetal cardiac activity is typically first detected on transvaginal ultrasound when the CRL reaches 2 to 4 mm, corresponding to approximately 5.5 to 6 weeks gestation.
Question 6: What is the intradecidual sign on early pregnancy ultrasound?
- A small gestational sac embedded eccentrically within the decidua before a double sac is formed (Correct answer)
- A sign of miscarriage
- The appearance of a cornual pregnancy
- Normal cervical mucus
Correct answer: A small gestational sac embedded eccentrically within the decidua before a double sac is formed
The intradecidual sign is a small early gestational sac seen embedded off-center within the endometrial decidua, supporting intrauterine implantation before the double sac is clearly visible.
PU First Trimester Ultrasound and Dating 1
What is the earliest structure visualized on transvaginal ultrasound in a normal intrauterine pregnancy?