You’ve probably noticed this pattern in Q-banks: the stem screams one diagnosis, but the answer choices are all “pregnancy-related bleeding + abnormal labs” look-alikes. Gestational trophoblastic disease (GTD) is a perfect example—because on Step 1/2, the right answer is often obvious, but the score boost comes from knowing why every other option is wrong.
The Vignette (Q-Bank Style)
A 24-year-old G1P0 presents with vaginal bleeding and severe nausea/vomiting at 10 weeks’ gestation. She reports passing “grape-like” tissue. She has no prenatal care. Vitals: BP 148/92 mm Hg. Exam: uterus is larger than expected for dates. Labs show markedly elevated -hCG. Transvaginal ultrasound shows a diffuse echogenic intrauterine mass with multiple small cystic spaces, and no fetus.
What is the most likely diagnosis?
A. Complete hydatidiform mole
B. Ectopic pregnancy
C. Threatened abortion
D. Choriocarcinoma
E. Placenta accreta spectrum
Correct Answer: A. Complete hydatidiform mole
Why it fits
A complete mole is classic for:
- First-trimester bleeding
- Uterus large for gestational age
- Very high -hCG
- Severe hyperemesis gravidarum (hCG stimulates nausea pathways)
- Early-onset preeclampsia (< 20 weeks is a huge red flag)
- Ultrasound: “snowstorm” / “cluster of grapes” (diffuse trophoblastic proliferation + hydropic villi)
- No fetus present
Pathophysiology & genetics (high-yield)
Complete mole typically arises when an “empty” ovum (no maternal nuclear DNA) is fertilized:
- By one sperm that duplicates → 46,XX (most common)
- Or by two sperm → 46,XY Key idea: Purely paternal genome → exuberant trophoblast + placental tissue, no embryo.
Complications to know
- Theca-lutein cysts (ovarian hyperstimulation from high hCG)
- Hyperthyroidism (hCG can weakly stimulate TSH receptor → ↑ free T4)
- Progression to gestational trophoblastic neoplasia (GTN), including invasive mole or choriocarcinoma
Next best step (Step 2 management pearls)
After suction curettage:
- Serial quantitative -hCG until undetectable, then continue monitoring per protocol
- Reliable contraception during follow-up (to interpret hCG correctly)
- If hCG plateaus/rises → evaluate/treat for GTN (often methotrexate or actinomycin D depending on risk)
Why Each Distractor Is Wrong (and How They Try to Trick You)
B. Ectopic pregnancy
Why it’s tempting: bleeding + pregnancy + abnormal hCG is a common Step trap.
Why it’s wrong here:
- Ectopic often has unilateral pelvic pain, adnexal tenderness, and sometimes shoulder pain from hemoperitoneum
- Ultrasound in ectopic typically shows:
- No intrauterine pregnancy when hCG is above the discriminatory zone (often ~– mIU/mL depending on institution), and/or
- An adnexal mass or “tubal ring”
- Does not cause “snowstorm” intrauterine pattern
- Uterus size is usually normal or small, not dramatically enlarged
High-yield discriminator:
- Mole = intrauterine “snowstorm,” very high hCG, big uterus
- Ectopic = empty uterus + adnexal findings, hCG rises abnormally (often slower), pain prominent
C. Threatened abortion
Definition: Vaginal bleeding before 20 weeks with closed cervical os and a viable intrauterine pregnancy.
Why it’s wrong here:
- Threatened abortion implies fetal cardiac activity and products of conception still present normally
- hCG is not typically “markedly elevated” (it may be appropriate for gestational age)
- Ultrasound should show a gestational sac +/- fetal pole, not diffuse cystic trophoblastic tissue
- “Passing grape-like tissue” points away from threatened abortion and toward molar tissue
Quick table: bleeding in early pregnancy
| Condition | Cervical os | Ultrasound | Key clue |
|---|---|---|---|
| Threatened abortion | Closed | Viable IUP | Mild bleeding, reassuring US |
| Inevitable abortion | Open | Products may be present | Cramping + open os |
| Incomplete abortion | Open | Retained products | Heavy bleeding |
| Complete abortion | Closed after passage | Empty uterus | Pain/bleeding improve |
D. Choriocarcinoma
Why it’s tempting: also a trophoblastic disease with high hCG.
Why it’s wrong here:
- Choriocarcinoma usually presents after a molar pregnancy, abortion, ectopic, or term pregnancy with:
- Persistent or rising hCG after evacuation
- Irregular bleeding
- Symptoms from metastases (lungs most common → cough, hemoptysis)
- Ultrasound in choriocarcinoma: typically a heterogeneous uterine mass, not classic diffuse hydropic villi pattern
- Histology (high yield): no chorionic villi in choriocarcinoma (just sheets of malignant cytotrophoblast + syncytiotrophoblast)
Step takeaway:
- Complete mole = chorionic villi present (hydropic)
- Choriocarcinoma = no villi, aggressive hematogenous spread (lungs/brain)
E. Placenta accreta spectrum
Definition: Abnormal adherence/invasion of placenta into myometrium due to defective decidua basalis.
Why it’s wrong here:
- Typically presents in third trimester or at delivery with:
- Failure of placental separation
- Massive postpartum hemorrhage
- Major risk factors:
- Prior C-section
- Placenta previa
- Prior uterine surgery/curettage
- It’s not a classic cause of first-trimester severe hyperemesis, extreme hCG, or “snowstorm” ultrasound
High-yield pairing: placenta accreta is a delivery/postpartum hemorrhage diagnosis, not an early pregnancy hCG-driven syndrome.
High-Yield GTD Rapid Review (What Step Loves)
Complete vs Partial Mole (must-know)
| Feature | Complete mole | Partial mole |
|---|---|---|
| Karyotype | 46,XX (most) or 46,XY | 69,XXX/XXY/XYY |
| Genetic origin | Paternal only (empty egg + sperm duplication) | Two sperm + normal ovum |
| Fetus | Absent | Often present (abnormal) |
| hCG level | Very high | Mild–moderately elevated |
| Uterus size | Often large for dates | Often normal/small |
| US | “Snowstorm,” no embryo | Abnormal placenta + fetus may be seen |
| Malignancy risk | Higher | Lower |
Classic “bonus” associations
- Preeclampsia before 20 weeks → think molar pregnancy
- Hyperemesis gravidarum + very high hCG → GTD on the list
- Hyperthyroidism signs (tremor, tachycardia) → hCG cross-reactivity at TSH receptor
- Theca-lutein cysts → high hCG effect on ovaries
Post-evacuation follow-up (frequent Step 2 angle)
- Serial hCG until negative; rising/plateau suggests GTN
- Contraception to avoid confusing hCG trends
- Choriocarcinoma is highly chemo-sensitive (often excellent prognosis when treated)
How to “Test-Writer Proof” Yourself
When you see first-trimester bleeding, quickly sort by:
- Where is the pregnancy? (IUP vs ectopic)
- Is there a fetus? (present vs absent)
- How high is hCG relative to gestational age?
- Any “weird” systemic clues? (early preeclampsia, hyperemesis, hyperthyroid)
If you can explain why the distractors don’t fit, you’ll stop missing the “easy” GTD questions for preventable reasons.