Gestational Pathology — Placenta, Ectopic, Molar Pregnancy

Ectopic Pregnancy — Abnormal Implantation Site

• Pathogenic mechanism: Embryonic implantation occurs outside the uterine cavity, most commonly in the fallopian tube (tubal pregnancy, 95% of ectopic cases). Abnormal tubal peristalsis, compromised mucosal integrity, or altered trophoblastic invasion allows implantation in ectopic locations (interstitial, cervical, ovarian, abdominal).
• Morphology: Trophoblastic invasion damages the thin-walled tubal mucosa, leading to hemorrhage into the tubal lumen and surrounding serosa. Unlike intrauterine implantation, the tube lacks the decidualized endometrium necessary for nutrient supply, resulting in poor placental development and rupture typically at 6-12 weeks.
• Tissue response: Absence of the endometrial-trophoblastic interface characteristic of normal pregnancy prevents adequate hemostasis; erosion into tubal vessels causes catastrophic hemorrhage into the peritoneal cavity.

Molar Pregnancy — Abnormal Trophoblastic Proliferation (Complete Mole)

• Genetic basis: Complete hydatidiform mole arises from androgenetic diploid origin—typically an empty egg (0n) fertilized by a single sperm that duplicates its chromosomes (46,XX or 46,XY, genetically paternal). This results in complete absence of fetal tissue and excessive trophoblastic proliferation unrestrained by normal biparental gene imprinting.
• Imprinting defect pathophysiology: Maternal imprinting genes (e.g., CDKN1C, PHLDA2) that normally suppress trophoblastic growth are absent. Paternal imprinting promotes placental expansion; unopposed expression of paternally-expressed growth factors (e.g., IGF2) drives uncontrolled proliferation of syncytiotrophoblast and cytotrophoblast.
• Morphological consequence: Diffuse hydropic swelling of all chorionic villi with marked trophoblastic hyperplasia (complete encirclement of villi by cytotrophoblast), absent or rudimentary fetal parts, markedly elevated β-hCG (>100,000 mIU/mL typical). Villi exhibit "grape-like" appearance grossly and "lacy" trophoblastic pattern microscopically.

Molar Pregnancy — Partial Mole Pathophysiology

• Genetic origin: Triploidy (69,XXY or 69,XXX, biparental contribution) resulting from fertilization of a normal egg by two sperm or by diploid sperm. Contains both fetal tissue and abnormal trophoblastic tissue; the presence of maternal genetic material permits some fetal development.
• Imprinting balance disrupted: Excess paternal chromosomes relative to maternal imprinting signals permits trophoblastic proliferation but does not completely suppress fetal development. Results in focal villous edema rather than diffuse swelling, scattered trophoblastic hyperplasia, and recognizable (though abnormal) fetal parts.
• Malignant potential reduced: Lower β-hCG levels; risk of GTN approximately 1-5% versus 15-20% for complete moles.

Placental Abnormalities

• Placental insufficiency: Intrinsic abnormalities in villous development (hypoplasia, dysplasia) or trophoblastic invasion defects lead to impaired nutrient and gas exchange, resulting in intrauterine growth restriction (IUGR) and fetal hypoxia.
• Abnormal invasion: Defective cytotrophoblastic remodeling of uterine spiral arteries results in high-resistance placental blood flow. Inadequate trophoblastic invasion underlies preeclampsia and placental abruption.

Ectopic Pregnancy

• Tubal pathology: Prior salpingitis (sexually transmitted infection, pelvic inflammatory disease), endometriosis, adhesions, congenital tubal anomalies
• Impaired tubal motility: Smoking (reduces ciliary function), hormonally mediated peristalsis dysfunction
• Intrauterine device (IUD) use: Increases relative risk; prevents intrauterine implantation but does not prevent extrauterine implantation
• Prior ectopic pregnancy: 10-25% recurrence risk
• Assisted reproductive technology: Increased risk due to placement of embryo and multiple implantation sites
• Pelvic/abdominal surgery: Adhesions compromise normal anatomical relationships
• Age >35 years: Cumulative tubal pathology

Complete Hydatidiform Mole

• Advanced maternal age (>40 years): Strong epidemiological association; may reflect aneuploidy in oocyte and aberrant fertilization
• Prior molar pregnancy: 1-2% recurrence risk; may indicate predisposition to abnormal oogenesis or fertilization
• Low socioeconomic status: Nutritional factors may increase risk of abnormal meiosis
• Geographic variation: Higher incidence in Asia and Latin America; genetic and nutritional factors proposed

Partial Hydatidiform Mole

• Triploidy from polyspermy: Risk factors related to fertilization anomalies
• Advanced maternal age: Lesser association than complete moles
• IVF pregnancy: Increased relative risk of triploidy

Ectopic Pregnancy

• Abnormal vaginal bleeding: Often described as dark, "prune juice" appearance due to endometrial sloughing without ongoing pregnancy hormonal support; distinct from normal heavy menstrual bleeding
• Pelvic or abdominal pain: Initially localized to side of ectopic implantation; becomes generalized and severe with tubal rupture, accompanied by acute peritoneal irritation (guarding, rebound)
• Palpable adnexal mass: Found on pelvic examination in up to 50% of cases; represents ectopic gestational sac with surrounding hemorrhage
• Hemodynamic instability: With rupture and hemorrhage—tachycardia, hypotension, syncope, acute abdomen
• β-hCG level: Positive but typically lower than intrauterine pregnancy of same gestational age; shows slower rise in serial measurements (doubling time >48 hours suggests abnormal pregnancy)
• Transvaginal ultrasound findings: Absence of intrauterine gestational sac despite positive β-hCG; adnexal mass with ring of echogenicity or yolk sac; free pelvic fluid (indicating hemorrhage)

Complete Hydatidiform Mole

• Vaginal bleeding: First trimester—typically massive, persistent; passage of grape-like vesicular tissue pathognomonic
• Markedly excessive uterine enlargement: Uterine size disproportionate to gestational age ("larger than dates"); due to massive trophoblastic proliferation and intrauterine blood accumulation
• Hyperemesis gravidarum: Exaggerated morning sickness; correlates with extremely high β-hCG levels (often >100,000 mIU/mL)
• Hyperthyroidism symptoms: Tachycardia, heat intolerance, tremor; due to β-hCG's weak thyroid-stimulating activity (structural homology to TSH) at extremely high concentrations
• Preeclampsia in first/early second trimester: Unusual timing (typically occurs after 20 weeks); reflects abnormal trophoblastic invasion and cytokine release; presents with hypertension and proteinuria before fetal viability possible
• Respiratory distress: From trophoblastic embolization of trophoblastic tissue into pulmonary vasculature or from pulmonary edema secondary to preeclampsia
• Vaginal ultrasound: Pathognomonic "bunch of grapes" or "snow-storm" appearance—heterogeneous echogenic mass filling uterine cavity with vesicles of varying size, no fetal pole, bilateral theca lutein cysts on ovaries (from excessive hCG stimulation)

Partial Hydatidiform Mole

• Vaginal bleeding: Often less dramatic than complete mole
• Modest uterine enlargement: Less pronounced than complete moles
• Lower β-hCG: Typically <50,000 mIU/mL
• Fetal tissue present: May have recognizable fetal skeleton or cardiac activity (though abnormal)
• Preeclampsia: Less common than with complete moles

Placental Insufficiency

• Poor fetal growth: Reduced birth weight, oligohydramnios
• Nonreactive fetal heart rate tracings: Decreased variability, late decelerations

Histopathological Diagnosis (Gold Standard)

Complete Hydatidiform Mole — Characteristic Microscopy

• Diffuse hydropic swelling: ALL chorionic villi uniformly enlarged with clear, edematous stroma
• Circumferential trophoblastic hyperplasia: Cytotrophoblastic layer completely surrounds villi (contrasts with normal focal trophoblast at tips); hyperchromatic nuclei with increased mitotic figures
• Syncytial abnormalities: Varying thickness, areas of syncytial necrosis, trophoblastic basement membrane intact
• Absence of fetal vasculature: Villi lack blood vessels characteristic of normal placenta
• No fetal tissue: Complete absence of embryo, amnion, umbilical cord
• Morphology summary: "Lacy network of trophoblast surrounding hydropic villi"

Partial Hydatidiform Mole — Characteristic Microscopy

• Focal villous edema: Only some villi enlarged; normal-sized villi interspersed with hydropic villi (creating heterogeneous appearance)
• Focal trophoblastic hyperplasia: Cytotrophoblast does not completely encircle villi; normal architecture present in areas
• Presence of fetal tissue: Recognizable fetal parts (skeleton, cardiac tissue), fetal red blood cells, umbilical cord elements
• Fetal vasculature present: In non-edematous villi
• Trophoblastic basement membrane: Usually intact but may show areas of abnormality

Flow Cytometry / Molecular Karyotyping

• Complete mole: Diploid pattern (46,XX or 46,XY); all DNA paternal origin on imprinting studies
• Partial mole: Triploid (69,XXY or 69,XXX) on flow cytometry; biparental origin on imprinting analysis

Laboratory Diagnosis

• β-hCG quantitation:
• Complete mole: >100,000 mIU/mL (often 500,000-2,000,000 mIU/mL)
• Partial mole: <50,000 mIU/mL
• Normal early intrauterine pregnancy: doubles every 48-72 hours; slower rise suggests ectopic or molar pregnancy
• Free β-hCG and α-fetoprotein (AFP): Elevated; abnormal ratios compared to normal pregnancy
• Thyroid function tests: Elevated free T4, suppressed TSH in complete moles (from β-hCG stimulation)
• Preeclampsia labs: Hypertension, proteinuria (≥1+ on urinalysis or ≥300 mg/24 hours), elevated LDH, low platelets in severe cases

Imaging Diagnosis

• Transvaginal ultrasound (preferred modality):
• Ectopic pregnancy: Adnexal gestational sac (ring of echogenicity with yolk sac), no intrauterine sac, free fluid in pelvis
• Complete mole: Heterogeneous echogenic mass ("snow-storm" or "bunch of grapes" pattern), no fetal pole, bilateral theca lutein cysts (>2 cm, multiple, fluid-filled), normal-sized or enlarged uterus
• Partial mole: Hydropic placental tissue with recognizable fetal parts, fetal cardiac activity (abnormal heart rate or rhythm), abnormal amniotic fluid volume
• Doppler ultrasound: Increased peak systolic velocity and abnormal impedance in molar pregnancy
• Pelvic MRI: Assists in characterizing adnexal masses and hemorrhage in ectopic pregnancy; less commonly used

Gross Pathology Examination

• Ectopic pregnancy specimen: Tubal dilation with hemorrhagic contents; thin, dilated tube may rupture during handling; trophoblastic tissue (chorionic villi) identified within tubal lumen
• Complete mole curettage specimen: Grape-like vesicular tissue, friable, dark red from hemorrhage; mass of tissue without recognizable fetal parts; often described as filling curettage cannula
• Partial mole specimen: Mixed appearance of hydropic tissue and normal-appearing placental tissue; fetal parts identifiable

Diagnostic Criteria Integration

• Complete mole: Histology (diffuse hyperplasia, all hydropic villi) + β-hCG >100,000 + ultrasound (snow-storm, no fetus, theca lutein cysts) + flow cytometry (diploid, paternal origin)
• Partial mole: Histology (focal hyperplasia, heterogeneous edema, fetal tissue) + β-hCG typically <50,000 + fetal parts on imaging + flow cytometry (triploid)
• Ectopic pregnancy: No intrauterine gestational sac at β-hCG >2,000 mIU/mL on high-quality transvaginal ultrasound; positive β-hCG with adnexal mass or free pelvic fluid

Ectopic Pregnancy

Medical Management (First-Line for Stable Patients with Unruptured Ectopic)

• Methotrexate (MTX) 50 mg/m² IM single dose:
• Mechanism: Inhibits dihydrofolate reductase, blocking thymidylate synthase and nucleotide synthesis; arrests rapidly dividing trophoblastic cells
• Success rate: 85-95% for unruptured ectopic <3.5 cm without fetal cardiac activity and β-hCG <5,000
• Rationale: Preserves tubal integrity and preserves future fertility compared to surgery
• Follow-up: β-hCG measured at days 4 and 7; should decline by ≥15%; additional MTX dosing or surgery if inadequate response
• Contraindications: Immunocompromise, renal/hepatic dysfunction, active pulmonary disease, peptic ulcer, inability to follow-up

Surgical Management (Indications and Approach)

• Emergency laparotomy with salpingostomy or salpingectomy:
• Indications: Ruptured ectopic with hemodynamic instability, free hemorrhage, patient in shock, unable to comply with medical management
• Salpingostomy (linear incision, product of conception expressed): Preferred if future fertility desired, patent contralateral tube; lower success if ectopic >2 cm
• Salpingectomy (removal of entire tube): Indicated if tube severely damaged, recurrent ectopic in same tube, hemodynamically unstable (faster operative time)
• Laparoscopic approach: Preferred if patient stable; allows visualization, assessment of contralateral tube and pelvis; lower morbidity than open approach

Expectant Management (Highly Selective)