Carrie Underwood is pregnant.

The 'Before he Cheats' hitmaker and her 38-year-old husband Mike Fisher - who already have three-year-old son Isaiah together - are ''over the moon'' to be expecting a new addition to their family.

Carrie said: ''Mike and Isaiah and I are absolutely over the moon and excited to be adding another little fish to our pond.''

The 35-year-old singer made her announcement when she told fans in an Instagram video that the tour to support her upcoming album, 'Cry Pretty', won't begin until May, eight months after the release of the record.

She said: ''You might be wondering or asking, 'Carrie, why is your tour starting in May?' ''

The camera then panned out to show Carrie was sitting under balloon letters spelling out the word ''Baby''.

The 'Dirty Laundry' singer - who didn't reveal when she is due to give birth - admitted life couldn't be better for her at the moment.

She said: ''This has just been a dream come true with album and baby news and all that stuff.

''We're just so excited and so just glad you guys can share in this with us and be a part of this with us.''

Carrie's announcement came just a few weeks after she admitted she was concerned she'd missed her chance to have a large family.

She said: ''I'm 35, so we may have missed our chance to have a big family.''

But the 'Remind Me' hitmaker hasn't completely given up on the idea of having more children, as she admits she's looked into some other options.

She added: ''We always talk about adoption and about doing it when our child or children are a little older. In the meantime, we're lucky to be a part of organisations that help kids, because our focus right now in our lives is helping as many kids as possible.''