She said: "I burst into tears at my first scan. It was the profile that got me: I think it looks like me,
"I was overcome with emotion, I don't know where it came from.
"I saw the baby wriggling away and burst into tears, crazily so. It suddenly felt real and it mustn't have done until that point."
Kimberley and Justin, 31, are not planning to find out the gender of their unborn tot as they would rather have an "amazing surprise" when he or she is born.
Speaking to the new issue of Britain's OK! magazine, Kimberley said: "We won't find out the sex - it's one of those amazing surprises in life that you can't buy.
"I really want Justin to tell me. You need to be looking, as I'm going to be desperate to know."
The 'Promise' singer also revealed her best friend and former bandmate Cheryl Cole wept when she told her the happy news.
She said: "Cheryl burst into tears of joy when I told her I was pregnant."