Every complication unique to monochorionic twins traces back to one fact: they share a single placenta and its vascular connections. This talk uses that shared circulation as the throughline for understanding twin-to-twin transfusion syndrome (TTTS), twin anaemia-polycythaemia sequence (TAPS), selective fetal growth restriction (sFGR), and twin reversed arterial perfusion (TRAP).

Starting with the placental vascular anatomy — arterio-arterial, veno-venous, and arterio-venous anastomoses — the talk shows how the presence, absence, and balance of these connections determines which complication develops, and how unequal placental sharing adds a second, independent risk factor. Real placental injection specimens and ultrasound cases illustrate each condition's mechanism, diagnostic criteria, and staging system, alongside current ISUOG surveillance schedules and management pathways, including fetoscopic laser therapy and cord occlusion.

The aim is a clear working framework: recognise chorionicity early, understand what drives each complication, and know when findings warrant referral for fetal therapy.