Melanie, who is married to footballer Theo Walcott, attended a photo call to officially mark her new role yesterday (30 January) and looked simply glowing.
The pregnant star covered her blooming tummy in a pretty high-waisted maternity skirt, which she teamed with a black top and a funky leather jacket.
Melanie topped off her yummy mummy look with thick black tights and black suede ankle boots, and she wore her blonde hair in a chic up 'do.
In December, Melanie and Theo announced their happy pregnancy news, saying: "We're both very excited."
The childhood sweethearts got engaged on New Year's Eve in 2011, after Theo popped the question at their Hertfordshire home.
They started dating after meeting at a local shopping centre when they were just 15 and married at an Italian castle in June last year.
Melanie returned to her home city of Southampton, Hampshire, to become patron of the Children's Air Ambulance charity, which is the UK's first dedicated air service for critically-ill babies and children.
She toured Southampton General Hospital Paediatric Intensive Care Unit with doctors, before having a look at the helicopter pad where the emergency helicopters land.
Melanie, said: "I'm proud to be asked to be the patron for the Children's Air Ambulance Service.
"I look forward to working with the team to help this charity grow into a truly national service so that every child on the UK mainland can have access to the service should they need it."
Melanie added: "It is fitting that my first formal duty is in my home town of Southampton where they have one of the best paediatric intensive care unit in the country."
Celebrities who have announced their pregnancies in 2014:
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