Molar Pregnancy (Quick and Dirty - Resident Level)

 Hydatidiform Mole


"Snowstorm" appearance of a complete mole on TVUS


Introduction:

Molar pregnancy, or a hydatidiform mole, is a type of gestational trophoblastic disease (GTD) that originates from abnormally proliferating placental tissue. 

  • Complete mole: one or two sperm fertilize an empty ovum → entirely paternal nuclear DNA
  • Partial mole: two or more sperm fertilize a viable ovum → triploid diandrous monogynic nuclear DNA



Evaluation:

Complete and partial moles tend to present somewhat differently. Partial moles behave more like a typical pregnancy initially, and they are often only diagnosed incidentally from histological evaluation of expulsed tissue following a spontaneous abortion. 

A partial mole = symptoms mimicking normal pregnancy

A complete mole has more distinguishable symptoms:
  • Vaginal bleeding - due to molar tissue separating from decidua
  • Very high levels of beta-hCG (often > 100,000 mIU/mL) → hyperemesis graviderum
  • Passage of tissue described as "grape-like" clusters
  • Symptoms of thyrotoxicosis - due to high beta-hCG which 
    • Tachycardia, palpitations, tremors, weight loss, anxiety, etc.
  • Signs a symptoms of pre-eclampsia
    • Hypertension, proteinuria, signs of end organ damage
  • Enlarged uterus, greater than would be expected for gestational age of a viable pregnancy

Workup:
  • Labs: quantitative beta-hCG
  • TVUS

Ddx:
  • Viable pregnancy
  • Thyrotoxicosis, hyperthyroidism
  • Hyperemesis gravidarum
  • Hydropic aborted fetus
  • Hypertension

Treatment: 

For those who wish to preserve fertility, a suction dilatation and curettage is first line. Oxytocin is also administered concurrently and several hours afterwards to reduce the risk of hemorrhage, and blood products should be available on standby.  

Rh immunoglobulin should be given to Rh- patients since the Rh antigen is expressed on the trophoblast. 

Hysterectomy is a good alternative if the patient has completed child-bearing and no longer desires future pregnancy. This has the added benefit of decreasing the likelihood of myometrial invasion with conversion to gestational trophoblastic neoplasia (GTN). 

Hysterotomy and induction are not recommended as they increase the chance of developing GTN.

After molar evacuation, consider giving prophylactic methotrexate. This decreases the risk of GTN by 3-8%. However, this should be weighed against the risks of using chemotherapeutic agents.

The patient should be on reliable contraception for at least one year.

Additionally, after molar evacuation, recheck beta-hCG every 1-2 weeks for a month and then monthly for a year to monitor for GTN. 

Normally, beta-hCG should rapidly fall to zero. A plateau or rise in beta-hCG is concerning for GTN. If this occurs, recheck beta-hCG in 48 hours to rule out a viable pregnancy. 


References:
1.
Cue L, Farci F, Ghassemzadeh S, Kang M. Hydatidiform Mole. In: StatPearls. StatPearls Publishing; 2025. Accessed February 28, 2026. http://www.ncbi.nlm.nih.gov/books/NBK459155/
2.
Skandhan AKP. Snowstorm sign (complete hydatiform mole) | Radiology Reference Article | Radiopaedia.org. Radiopaedia. doi:10.53347/rID-37546










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