Society and the media are putting new mothers under appalling pressure to lose their baby weight, according to a government minister who has also criticised the "disgraceful focus" on the Duchess of Cambridge's body following the birth of her son.

Jo Swinson, the minister for women and equalities – who is expecting her first child – said the media needed to rethink its attitude towards birth and women's bodies.

"At a time when new mums are focused on building bonds with their newborns, the media unhelpfully churns out a set of impossible standards on losing baby weight within ridiculous timeframes," she told the Sunday Times.

"We need to move away from the idea that women have to shed their baby weight quickly and that they're failing somehow if they don't. Surveys show this is a concern for two-thirds of new mothers."

Swinson said coverage of the duchess's weight showed just how extreme society's obsession with female physical perfection had become, and criticised OK! magazine for featuring an "exclusive duchess diet and shape-up plan" and running an interview with her fitness trainer, who claimed "her stomach will shrink straight back" after the birth.

"Publications like OK! magazine need to get some perspective," she said. "Fitting back into pre-pregnancy jeans is not the priority after childbirth."

Swinson, who chaired the all-party parliamentary group on body image and was a co-founder of the Campaign for Body Confidence, is working with the Department of Health on measures to help new mothers deal with such pressure.

"The government's body confidence campaign has put together a steering group of midwives, health visitors and other experts to look at how to raise awareness of the issue among health professionals," she said.

Health visitors would be trained to look out for depression caused by baby weight anxiety and to reassure new mothers that losing weight did not need to be a priority.

The parliamentary group, which is working to prevent negative body image and promote healthier attitudes towards people's bodies, found that physical appearance was the largest cause of bullying in schools.

Its inquiry also revealed that half of girls and a third of boys had been on a diet to change their shape by the age of 14, and that one in three men would sacrifice a year of life to achieve their ideal body.