The country star and Buchanan, who married in a sunrise ceremony in May 2012, will welcome the baby girl in November, reports People.
Owen told the publication that the couple were aware of Buchanan's pregnancy shortly after becoming engaged but chose to keep the news private for several reasons.
"We actually found out Lacey was pregnant after I had asked her dad for his permission. From the day I met her, there was no doubt in my mind I wanted to marry her, and we always knew we wanted a family," he explained.
"The way we saw it, the baby news was a bonus on top of the engagement, but we didn't want anyone to think we were getting married because Lacey was pregnant, and we wanted to celebrate our wedding first."
Buchanan added: "We didn't want to go public with it until we found out if it was a boy or a girl. The pregnancy was just something we wanted to keep for ourselves for a little while."