Which complication is unique to monochorionic twin pregnancies and results from unequal blood flow between twins?

Explanation

## Twin-to-Twin Transfusion Syndrome (TTTS) **Key Point:** TTTS is a unique complication of **monochorionic diamniotic or monoamniotic** twin pregnancies caused by unequal placental blood flow through arteriovenous anastomoses. ### Pathophysiology ```mermaid flowchart TD A[Monochorionic Placenta]:::outcome --> B[Vascular Anastomoses Present]:::outcome B --> C{Unequal Flow Distribution?}:::decision C -->|Artery-to-Vein| D[Donor Twin: Hypovolemia]:::urgent C -->|Artery-to-Vein| E[Recipient Twin: Hypervolemia]:::urgent D --> F[Donor: Anemia, FGR, Oligohydramnios]:::outcome E --> G[Recipient: Polycythemia, Polyhydramnios, CHF]:::outcome F --> H[TTTS Diagnosis]:::outcome G --> H ``` ### Diagnostic Criteria (Quintero Classification) **High-Yield:** TTTS is diagnosed when **both** of these are present: 1. Polyhydramnios in recipient twin (DVP ≥8 cm before 20 weeks, ≥10 cm after 20 weeks) 2. Oligohydramnios in donor twin (DVP <2 cm) ### Clinical Features | Feature | Donor Twin | Recipient Twin | |---|---|---| | Fluid volume | Oligohydramnios | Polyhydramnios | | Hemoglobin | ↓ (Anemia) | ↑ (Polycythemia) | | Growth | FGR, small | Larger | | Cardiac status | Normal | Cardiomegaly, CHF | | Urine output | ↓ | ↑↑ | | Outcome | Stillbirth risk | Hydrops, heart failure | **Clinical Pearl:** The **donor twin** (hypovolemic) is at higher risk of intrauterine death; the **recipient twin** (hypervolemic) is at risk of congestive heart failure and hydrops fetalis. ### Why TTTS is Unique to Monochorionic Twins **Mnemonic:** **TTTS = Two Twins, Two Circulations, Tangled Vessels** (vascular anastomoses exist only when placentas are fused) - **Dichorionic twins:** Separate placentas → no vascular anastomoses → **no TTTS** - **Monochorionic twins:** Shared placenta → arteriovenous anastomoses → **TTTS possible** ### Management 1. **Selective laser photocoagulation** of anastomoses (gold standard if <26 weeks) 2. **Amnioreduction** (symptomatic polyhydramnios) 3. **Serial ultrasound surveillance** (weekly or twice-weekly) 4. **Delivery** at 36–37 weeks if stable [cite:Williams Obstetrics 26e Ch 45]