The 31-year-old, who married her husband Nick Lachey in July 2011, announced that she is pregnant last month.
She has now explained on an appearance on VH1's Big Morning Buzz Live that she isn't using her hormones as "excuses" to make her husband do things.
However, she continued: "I am using them as an excuse as to why I'm such a b-i-t-c-h sometimes!
"I'll snap and then I'm like, 'Oh honey, it's the baby'. I'm a little quicker to snap, but I'm also quicker to apologise. He has been a gem!"
Lachey, who has described her pregnancy as "fun", recently revealed that she wants to be "health-conscious" for her baby.
> Nick Lachey: 'I will be wife Vanessa Lachey's birth coach'
> Vanessa Lachey on pregnancy: 'I always wanted a boy first'
Watch Vanessa Lachey speaking on Big Morning Buzz Live below: