4. 1st Trimester Obstetric/OB Ultrasound Protocol

Molar Pregnancy

A molar pregnancy is a tumor due to the uncontrolled proliferation of trophoblasts, which are cells that surround the blastocyst and later become the placenta. These “moles” are categorized into complete and partial.

Complete molesPartial moles
No fetal/embryonic tissueMay contain fetal structures, albeit abnormal ones
Abnormally elevated B-hCG levels: >100,000 mIU/mLNormal B-hCG levels


  • Vaginal bleeding
  • Exaggerated uterine size for gestational age
  • Hyperemesis
  • Pregnancy-induced hypertension

A molar pregnancy will appear on ultrasound as a “snowstorm” inside the uterus. The contents of the uterus are complex and heterogeneous and often contain many small cystic structures. In addition, there may be theca-lutein cysts in the ovaries which are thin-walled cystic structures (these are more common in 2nd-trimester complete moles).

Molar Pregnancy Snowstorm Appearance OB Obstetric Obstetrical Ultrasound
Molar pregnancy. Note the snowstorm appearance and the cystic structures.
Theca Lutein Cyst in Ovary OB Obstetric Obstetrical Ultrasound
Theca lutein cysts in the ovary.

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