The congresswoman continued to work up until the day before birth, voting Wednesday for the farm bill.
"Everybody's healthy, everybody's thrilled and very excited," said Gillibrand's spokeswoman, Rachel McEneny.
It was not immediately clear how soon Gillibrand would return to her official duties.
"They will play it by ear like any new parents," said McEneny.
Gillibrand won an upset victory in 2006 over Republican incumbent John Sweeney to represent a congressional district that stretches north and south of the state capital of Albany. The district leans heavily Republican, and she has sought to steer a centrist course in Congress while also raising millions of dollars for what could be a tough re-election fight this year.
