The 30-year-old and husband Brad McAtee are "beyond excited" to be having a baby boy.
Wirkus and McAtee shared the news in Instagram posts Sunday. The couple announced their baby's sex at a celebration with family and friends in Palm Springs, Calif.
"Baby Boy McAtee coming May 2019 #itsaboy #morningsicknessisreal," Wirkus captioned a slideshow of photos from the event.
"Beyond excited to welcome Baby BOY McAtee in May 2019 #itsaboy," McAtee added on his own account.
Wirkus' twin sister and "Summer House" co-star, Lauren Wirkus, celebrated the news in an Instagram post Monday.
"Guys in case you missed @ashleynmcatee @bradmcatee big news WE'RE HAVING A BABY!! #itsaboy," she wrote.
Wirkus and McAtee will celebrate their three-year wedding anniversary Nov. 21.
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Wirkus called McAtee her "best friend" while ringing in their two-year anniversary in 2017.
"We have gone through some not so typical situations as a married couple and many people might say we are not 'normal' but I can tell you that when you marry your Best Friend it truly is the best!" she wrote.
"Summer House" follows Wirkus, Lauren and several of their friends as they share a summer house in Montauk, N.Y.
The Bravo series premiered its second season in January.
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