And to ensure everything went smoothly, the actress "hired several professionals".
The mother-of-three announced Mae's arrival with a picture from the birth, which was captioned: "Mae James Bair - We LOVE you beauty 3-24-21 (sic)"
Whilst Matthew wrote in his own post: "Mae James Bair 3/24/21 (sic)"
Meanwhile, Hilary previously revealed her son was being "so helpful" ahead of the baby's arrival as she praised him for always helping.
The 33-year-old star said: "It's been so cool to be pregnant and have an almost nine-year-old. [Luca is] super compassionate and understanding of the fact that I'm moving a little slower and don't have as much energy as normal. He's so helpful. He jumps to help me when something spills in the kitchen and also great with helping me with bags from the car.