“I wouldn’t say I’m back in shape yet," she said. "Everything changes when you get older. It was different when I was 31 with the first one and now being 36 with the fourth one.”
She is spending time on the treadmill and eating sensibly to try and get back in shape as she fears she will remain bigger forever if she doesn’t work on it now.
“I think that if you wait too long and it sticks there it stays that way forever," she said. "I have to be motivated.”
Meanwhile, her husband Seal has also spoken out about the family, admitting he was initially unsure of how having another baby would affect their lives.
“It’s a funny thing, having another child, because you have three kids who you love dearly and you think to yourself how could you possibly find any more love to give anyone else?” he told Celebrity Baby Blog.
“The first time you hold your baby in your arms there is this overwhelming sense of otherworldliness that is very, very difficult to describe.”
Seal and Heidi are exhausted from looking after their newborn – but agree it’s worth it.
“Sleep deprivation is kind of pretty much neutralised by what I call the amnesia gene," Seal added. "They look at you and you forget that when you have more kids.”