McMorris Rodgers, a member of House leadership, and her husband, Brian Rodgers, announced the news on Friday.
McMorris Rodgers, who represents the Spokane region and Eastern Washington, is the first woman to give birth twice while a member of Congress.
Her third child is due in December.
McMorris Rodgers says she plans to run for re-election next year and remain the GOP conference chairwoman. Her other children are 6-year-old Cole and 2-year-old Grace.
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