A woman with twin pregnancy undergoes ultrasound at 12 weeks. A triangular projection of chorionic tissue extending into the base of the intertwin membrane is seen. This finding indicates:
- A Dichorionic diamniotic twinning ✓
- B Monochorionic diamniotic twinning
- C Conjoined twins
- D Twin reversed arterial perfusion sequence
Correct answer: A. Dichorionic diamniotic twinning
Explanation
The lambda or twin peak sign is a wedge of chorion extending between the layers of the intertwin membrane and confirms dichorionicity. It is most reliable between 6 and 9 weeks. In monochorionic twins the membranes meet the placenta in a thin T configuration (T sign) because only two amnions abut. Chorionicity determines prenatal management because monochorionic twins carry risks of twin transfusion syndrome and selective growth restriction that dichorionic pairs do not.
Reference: Callen's Ultrasonography in Obstetrics and Gynecology, 6th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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