Blake Lively has hit out at people who ''celebrate'' mothers dropping their pregnancy weight soon after birth.

The pregnant star - who has 18-month-old daughter James with husband Ryan Reynolds - insists body shamers should lay off women who have just given birth and be grateful that another baby has come into the world rather than focus on how someone looks.

She said: ''It's so unfair though, because it's so celebrated. It's like, this is what someone can look like after a baby. I think a woman's body after having a baby is pretty amazing.

''You don't need to be Victoria's Secret ready right away because you just did the most incredible miracle that life has to offer. I mean, you gave birth to a human being.

''So I would really like to see that celebrated.''

Despite this, the 28-year-old stunner had to slim down fairly quickly after giving birth to James to portray bikini-clad medical student Nancy Adams in thriller movie 'The Shallows'.

Speaking about getting into shape for the role, she told Australian breakfast TV show 'Sunrise': ''I had to do a lot of endurance training - this was eight months after I had a baby.''

The blonde beauty hired a personal trainer to get back into shape and admitted the exercise did more for her than simply shed the baby weight she'd gained.

She said: ''I worked out with an amazing trainer Don Saladino. He kicked my butt. It was also eight months after having a baby so my body was already completely different than what it normally was.

''Not just aesthetically but also your muscles are different, your body, everything is just shifted and changed.''