Hannigan and her husband and fellow "Buffy the Vampire Slayer" alum, Alexis Denisof, welcomed their first child on March 24. That just also happens to be Hannigan's birthday (she turned 35). People reports that the baby is a girl named Satyana Denisof.
It's the first child for the couple, who have been married for 5 1/2 years.
"How I Met Your Mother" opted not to write Hannigan's pregnancy (nor that of co-star Cobie Smulders) into the show, instead opting to have fun with hiding the actresses' bellies with loose clothing and objects in the foreground -- and in one case, letting Hannigan show hers off as her character, Lily, finishes a hot dog-eating contest.
The show also tweaked its schedule slightly to let Hannigan finish her work for the season a little early. She wrapped Lily's part in early March.
Smulders, by the way, is due to have her baby later this spring.