The Obsessed star and her husband, writer/actor Hayes MacArthur, announced Larter was expecting their first child in July (10), and the couple has kept the baby's sex under wraps.
But Larter spilled the secret on comedian Jimmy Fallon's U.S. late night show on Thursday (09Sep10), when the funnyman presented her with a pair of onesies - one pink and one blue.
Snatching the blue baby suit, she shouted the news and delivered a raunchy quip: "We're having a baby boy! Yes, I have a little penis inside of me."
The Obsessed star and her husband, writer/actor Hayes MacArthur, announced Larter was expecting their first child last week (20Jul10), less than a year after exchanging vows (Aug09).
But Larter, 34, admits she kept the exciting news under wraps for months before stepping out with her growing baby bump, because she wanted to enjoy the early stages of her pregnancy in private.
She says, "It was a very private time for me and my husband and something that I just wasn't ready to share, so we actually left the country for a while.
"This was something that I wasn't ready to share yet. So we came back from Europe, and I said to my husband, 'I just want to go to lunch with my girlfriends. I just want to live my life.' I was four months (pregnant) and it was just time to start living my life."
The baby is due this winter (10).
The couple married at the Planet Hollywood Resort & Casino, with their one-year-old son Valentine among the intimate wedding party.
Rajskub wore an ivory wedding gown designed by Nicole Miller, according to People.com.
She says, "Our wedding was beautiful, spontaneous and intimate... We are so excited to officially be husband and wife.
The newlyweds share a wedding anniversary with Ali Larter and Hayes MacArthur, who wed in Maine, and Mark Wahlberg and Rhea Durham, who tied the knot in Beverly Hills.
The actress wore a stunning white plunge-neck dress as she wed South African musician Abri van Straten on her farm surrounded by close friends and family.
Bauer tells RadarOnline.com, "On the morning of the wedding I woke up to rain but even the weather played along as the relatives arrived. The sky cleared, the sun came out and we had the most perfect wedding. We are very happy.
The newlyweds share an anniversary with three other Hollywood couples who wed on Saturday - Ali Larter and Hayes MacArthur married in Maine, Mark Wahlberg and Rhea Durham tied the knot in Beverly Hills and Mary Lynn Rajskub and Matthew Rolph walked down the aisle in Las Vegas.
The couple wed in Kennebunkport, Maine in front of family and friends.
Actress Amy Smart, Larter's best friend, was among the guests.
The newlyweds will share their wedding anniversary with Mark Wahlberg and Rhea Durham, who married in Beverly Hills on Saturday.
The Heroes star and her husband-to-be will exchange vows on his family property in Kennebunkport, according to In Touch magazine.
Larter's best friend, actress Amy Smart, will be among the wedding party.
A source tells the publication, "Hayes is really excited to spend time with a lot of his old buddies that he played football with at Bowdoin College in Maine and Ali just wants a dream wedding and for everything to be perfect.
The couple won't be the first celebrity pair to wed in Maine this summer - American Idol judge Kara Dioguardi exchanged vows with her new husband Mike McCuddy there earlier this month (05Jul09).