MELBOURNE, Australia - Serena and Venus Williams have pulled out of women's doubles at the Australian Open, where they've won four titles.

The Williams sisters were scheduled to play their first-round match Wednesday against Anabel Medina Garrigues of Spain and Yaroslava Shvedova of Kazakhstan.

A tournament official confirmed the Williams sisters had withdrawn, but did not specify a reason.

Both sisters won their first-round singles matches in singles on Tuesday.