Differential Diagnosis for 6-week OB Gestational Sac with Yolk Sac but No Fetal Pole

• Single Most Likely Diagnosis
  • Anembryonic Pregnancy (Blighted Ovum): This condition is characterized by the development of a gestational sac and sometimes a yolk sac, but without the formation of an embryo. It's a common cause of early pregnancy loss and fits the given ultrasound findings.
• Other Likely Diagnoses
  • Missed Abortion: This refers to a nonviable pregnancy that has not been expelled from the uterus. The absence of a fetal pole at 6 weeks could indicate a missed abortion, especially if there are no signs of embryonic development.
  • Delayed Embryonic Development: It's possible that the embryo is simply developing more slowly than expected. However, the presence of a yolk sac without a visible fetal pole at 6 weeks gestation makes this less likely.
• Do Not Miss Diagnoses
  • Ectopic Pregnancy: Although less likely given the presence of a gestational sac in the uterus, an ectopic pregnancy must always be considered, especially if there's any suspicion of abdominal pain or bleeding. A pregnancy test and possibly a laparoscopy might be needed to rule this out.
  • Molar Pregnancy: A molar pregnancy, also known as hydatidiform mole, is a rare condition where the placenta becomes abnormal. While it typically presents with a "snowstorm" appearance on ultrasound, early on it might not be distinguishable from a normal pregnancy or anembryonic pregnancy, making it crucial not to miss.
• Rare Diagnoses
  • Twin Pregnancy with Vanishing Twin: In the case of a twin pregnancy, one embryo might not develop or could be resorbed, leaving behind a single gestational sac with possibly a yolk sac but no visible fetal pole for the vanished twin.
  • Pseudogestational Sac: This can occur in the context of an ectopic pregnancy where a decidual reaction in the uterus mimics a gestational sac. However, the presence of a yolk sac makes this less likely, as pseudogestational sacs typically do not contain a yolk sac.