TENNIS star Serena Williams has given birth to a baby girl.

According to US reports, the world's number on tennis player welcomed her first child with her fiancé, Reddit founder Alexis Ohanian. 

Williams, the U23-time Grand Slam singles champion, announced she was pregnant in April.

The 35-year-old athlete said she had "planned on winning Wimbeldon" this year, until she discovered she was pregnant.

She has said she would return to competitive tennis in January, to defend her Australian Open title, which she won while newly pregnant.