170 Obstetrics and Gynecology Board Review •••
❍ What is the discriminatory size of the gestational sac (MSD) at which one would expect to see the yolk sac?
- MSD = 8 mm via TVUS (5.5 weeks).
- MSD = 20 mm via transabdominal ultrasound (7 weeks).
❍ What are several reasons for an irregular appearing gestational sac?
Uterine contractions, enlarged bladder, fibroids, implantation bleed, and failed pregnancy.
❍ What structure is the arrow pointing to in the ultrasound image?
Yolk sac.❍ What are the three known functions of the yolk sac?
(1) Provides nutrients for the embryo.
(2) Initial site of hematopoiesis.
(3) Contributes to developing gut and reproductive systems.
❍ Which is superior in confirming an IUP: a yolk sac within the gestational sac or the double decidual sac
sign (DDSS)?
The yolk sac within the gestational sac.
❍ After identification of a gestational sac, what is the next visible landmark for pregnancy dating?
The yolk sac.