Molar pregnancy (hydatidiform mole) is a premalignant gestational disorder and is included in the spectrum of disorders characterized as gestational trophoblastic disease. Molar pregnancies are classified as complete or partial based on morphologic and pathologic examination. Both complete and partial molar pregnancies have an abnormal placenta with enlargement and swelling of the chorionic villi and hyperplasia of the villous trophoblastic cells. Most molar pregnancies are complete and are characterized by generalized hydropic villous changes with no fetal tissue. Partial moles are characterized by a mixture of large hydropic villi and normal placental tissue and often have fetal tissue present. Gestational trophoblastic disease (GTD) is composed of a spectrum of neoplastic conditions derived from the placenta. Whereas hydatidiform moles, gestational choriocarcinoma, and placental site trophoblastic tumor (PSTT) are histologic diagnoses, postmolar gestational trophoblastic neoplasia (GTN) is defined by clinical and laboratory criteria. The disease entities included in GTD have a wide variation in behavior, but GTN specifically refers to those with the potential for tissue invasion and metastases.

The risk of malignant sequelae (GTN) for a complete mole is 7% to 30% and for a partial mole is less than 2.5% to 7.5%.

Hydatidiform mole

Complete molar pregnancy:

• 80% to 90% present with vaginal bleeding at 6 to 16 wk gestational age
• 28% with uterine enlargement greater than expected for gestational age
• 8% with hyperemesis gravidarum
• 1% with pregnancy-induced hypertension in the first or second trimester
• 9% to 25% with bilateral theca lutein cysts
• 15% will have a beta human chorionic growth hormone (beta hCG) >100,000 mIU/ml
• <10% with anemia

Partial molar pregnancy:

• 90% present with an incomplete or missed abortion
• 75% present with vaginal bleeding
• <10% will have a beta hCG of >100,000 mIU/ml

Complete molar pregnancy:

• Fertilization of an oocyte with absent or inactive maternal chromosomes (Fig. E1) and duplication of paternal chromosomes (85% to 90% are 46,XX) or, less commonly, fertilization of an empty oocyte with two sperm (46,XY)
• Diffuse villous edema and enlargement and trophoblastic proliferation (Fig. E2) with no development of a fetus

Complete mole, partial mole (Table E2), ectopic pregnancy, abortion (incomplete or spontaneous), normal intrauterine pregnancy

• Pelvic exam to evaluate for uterine size and bleeding
• Blood pressure to assess for (Fig E2) gestational hypertension or preeclampsia (systolic blood pressure >140 or diastolic blood pressure >90)
• Fig. E3 describes an algorithm for the diagnosis and management of molar pregnancy

Figure E3 Algorithm for the management of molar pregnancy.

CBC, Complete blood count; CT, computed tomography; hCG, human chorionic gonadotropin; PT, prothrombin time; PTT, partial thromboplastin time; WHO, World Health Organization.

From Gabbe SG: Obstetrics, ed 6, Philadelphia, 2012, Saunders.

• Quantitative beta hCG; significantly elevated levels >100,000 will raise suspicion for molar pregnancy
• Complete blood count (CBC) to assess for acute anemia from vaginal bleeding
• Comprehensive metabolic panel to evaluate for renal or liver disease
• Thyroid-stimulating hormone to evaluate for hyperthyroidism
• Urinalysis for proteinuria to evaluate for preeclampsia
• Type and screen to evaluate Rh status and to prepare for surgery
• Clotting studies (prothrombin time and international normalization ratio)

• Pelvic ultrasound (Figs. E4 and E5):
  1. Complete moles in the first trimester (Fig E5) will demonstrate a complex, echogenic, intrauterine mass containing many small cystic spaces that are secondary to swollen chorionic villi and no identifiable fetus. This is the classic “snowstorm” appearance (Fig. E6).
  2. Partial mole will show a thickened, hydropic placenta with fetal parts.
  3. Baseline chest x-ray to use for comparison if malignant trophoblastic disease develops.
• Magnetic resonance image (Fig. E7).

Surgical uterine evacuation with dilation and curettage (D&E) is the mainstay of management of a molar pregnancy, either partial or complete. Suction D&C is the preferred method in patients who desire future pregnancies. Ultrasound guidance and avoidance of sharp curettage may decrease the risk of uterine perforation.Pitocin infusion at a rate of 20 units/L can be considered after cervical dilation and can be continued for several hours postprocedure if bleeding persists. Hysterectomy should be considered in women older than 40 yr. Tables E3 and E4 summarize the management of hydatidiform moles.

D&E, Rh immune globulin if Rh negative

If pathology results are consistent with complete or partial mole, patients must be followed to evaluate for trophoblastic neoplasia. 7% to 30% of complete moles and 2.5% to 7.55% of partial moles can develop into trophoblastic neoplasia. Quantitative beta hCG should be followed weekly until three consecutive results show normal levels. After that, check quantitative beta hCG every month for a total of 6 mo. Patients should remain on reliable contraception during this time to prevent confusion from a rising beta hCG in the case of a new pregnancy.

Specific criteria by beta hCG have been established by International Federation of Gynecology and Obstetrics (FIGO) for diagnosis of postmolar gestational trophoblastic disease (see Tables E5, E6, and E7). Patients with pre-evacuation hCG greater than 100,000 mIU/ml, excessive uterine enlargement, theca lutein cysts greater than 6 cm, or older than 40 yr are at increased risk of postmolar gestational trophoblastic neoplasia. Patients with a complete or partial mole have a 1% to 2% incidence of second mole in subsequent pregnancies.

• If there is concern for a molar pregnancy, the patient should be managed by a gynecologist for uterine evacuation and follow-up.
• If there is a plateau or rise of the beta hCG during follow-up, the patient should be referred to a gynecologic oncologist for treatment with either further surgery or prophylactic chemotherapy.

Spontaneous Abortion (Related Key Topic)

Vaginal Bleeding During Pregnancy (Related Key Topic)