Fetty Wap's 1-Year-Old Daughter Undergoes Emergency Brain Surgery

Scary weekend for Fetty Wap and one of his baby mamas -- their 1-year-old daughter had to have emergency brain surgery ... TMZ has learned.

We're told Fetty and Alexis Skyy's daughter, Alaiya, needed the procedure to repair a malfunctioning implant in her brain that helps drain blood and fluids. Alaiya was born 3 months premature -- weighing just one pound -- and suffers from hydrocephalus, a condition that causes bleeding and fluid in the brain.

Sources connected to Alexis tell us she noticed something wrong on a flight from Atlanta to NY because Alaiya was excessively vomiting. We're told they bolted to the hospital where doctors began operating.