Twin-to-Twin Transfusion Syndrome (TTTS)

Twin-to-twin transfusion syndrome (TTTS) can occur only in twins who share one placenta (monochorionic). Because of blood vessel connections within the placenta, blood flows unevenly from one baby to the other: the "donor" baby is left with less blood and fluid, while the "recipient" baby gets overloaded. It develops in roughly 10-15% of monochorionic twin pregnancies — meaning most never experience it.

TTTS does not occur in twins with separate placentas (dichorionic) — so if you know your chorionicity, you already know whether this article concerns you. For monochorionic twins, this is exactly why NICE and ISUOG guidelines recommend an ultrasound every 2 weeks from 16 weeks: TTTS most often appears between weeks 16-26, and when caught early, treatment success is high.

Signs worth noticing: Your belly suddenly growing and feeling tight over a few days (from fluid buildup in the recipient baby's sac), a sudden increase in breathlessness, or early contractions. That said, TTTS is usually spotted on a routine scan before the mother feels anything — which is precisely why regular monitoring matters so much.

Diagnosis and staging are done by ultrasound: fluid differences between sacs, the appearance of the bladders and blood flows are assessed (Quintero staging). In early stages, close observation may be enough. In advanced stages, the most effective treatment is fetoscopic laser surgery — sealing the shared vessels in the placenta — and outcomes have improved markedly in recent years. Amnioreduction (draining excess fluid) can also be used when needed.

Dear mama, TTTS is an unsettling topic to read about — but remember: you are inside a monitoring system that knows this condition well. Keeping your two-week scan rhythm and telling your doctor about any sudden change in your belly are the two most powerful tools in your hands. The rest is the job of teams experienced in exactly this.