Twin-to-Twin Transfusion Syndrome: when one twin donates to the other

Sometimes, it's a feto-fetal transfusion syndrome (TTTS).

This only happens in twins who share the same placenta.
Vessels connect their circulations. If too much blood passes from one baby to the other, one grows less and has too little fluid, the other grows more, has too much fluid, and its heart can become strained.

It is detected by ultrasound every 2 weeks starting from 16 weeks of amenorrhea (WA).
If serious, it can be treated in utero with a laser to seal the connected vessels.

Without treatment, many babies do not survive.
After laser treatment, at least one child most often survives. Births often remain premature.