The M&S model, who is already mum to daughter Ava, three, is expecting another girl with partner Graham Quinn, but she said she doesn't mind having gained the extra weight during her current pregnancy.
The 32-year-old told UK magazine Now: 'It's more now! I was really jowly last time, so I'm sure I've got more weight to put on, too.
'But it's fine, it's the one time when you are meant to put on weight.”
She added: 'To be fair, I was heavier in college than I am pregnant, and in Hear'Say I was the same weight I am now.'
Klass also revealed that Ava is excited about having a new sister.
She said: 'Ava's been talking to her new sister through my belly button, saying good morning and goodnight every day.
'She can't wait to meet her sister, which is a change from when she first found out and told the doctor she wanted a rabbit.'