Health Secretary Andrew Lansley has confirmed that consultant-led maternity services are to be moved from Maidstone Hospital to the new Pembury Hospital.
It will leave Maidstone with a midwife-led birthing unit, despite opponents claiming lives could be put at risk.
Conservative MP for Maidstone, Helen Grant, said she was "appalled by the puzzling and irrational decision".
NHS managers have said the changes, which will take effect next year, are in the best interests of patients.
But Ms Grant said Mr Lansley's decision had failed to address the fact that local GPs "vehemently oppose plans to downgrade maternity services at Maidstone".
More than 20,000 people signed a petition to keep full maternity services at Maidstone Hospital, which was delivered to Downing Street.
Campaigner Peter Carroll said he feared the extra distance from Maidstone to Pembury could result in the loss of babies' lives.
He described it as a "very bad day for all the mums and mums-to-be in Maidstone".
"And most important of all it's a bad day for local democracy," he added.
Glenn Douglas, chief executive of the Maidstone and Tunbridge Wells NHS Trust, said the new unit at Pembury Hospital, near Tunbridge Wells, "with more consultant cover for midwifery and maternity care, outweighed the disadvantages of people having to travel a bit further for their care".
"It's only for the birth that people will have to travel. For the rest of their care they'll still be able to have that at Maidstone.
"And if they live on the other sides of Maidstone, they will also be able to choose to go to either Ashford or Medway as well," he said.