The 27-year-old was part of the team that won the silver medal at the Olympics in Beijing last year, Singapore's first for 48 years, and had promised that she will not allow her wishes to start a family getting in the way of competing in London.
She had agreed last month with Lee Bee Wah, president of the Singapore Table Tennis Association (STTA), that if she was not pregnant by the end of 2010 she would postpone her plans until after London.
But she has now announced that her and her husband, Li Chao, are expecting a bady.
Jiawei said: "I want to tell my friends and fans who have shown concern for me that I have a baby, I believe you will feel happy for me."
Jawei was born in Beijing but moved to Singapore when she was 14 and made her debut for adopted country when she was 18.
She won three gold medals at the 2002 Commonwealth Games in Manchester and two golds and a silver in Melbourne four years later.
But Jawei's greatest moment came in the city of her birth last year when, together with Feng Tianwei and Wang Yuegu, she took the silver medal in the team event at the Olympics.
The medal came 48 years after Tan Howe Liang won the country's first medal, a silver in weighlifting, at Rome in the 1960 Games.
photos Janos Schmidt