The American, 35, is due to give birth in the autumn, her representative has confirmed.
If accurate, that would mean Williams was around eight weeks pregnant while winning in Melbourne.
However, Williams will miss the rest of the season, having not played since the Australian Open, citing a knee injury.
Williams, who will return to world number one next week, would be eligible to retain her ranking under the WTA special ranking rule if she is ready to play her first tournament within 12 months of giving birth.
Former world number one Victoria Azarenka gave birth to her first child in December and is expected to return to competition at the end of July.
Belgium's Kim Clijsters, meanwhile, won the US Open in 2009 just 18 months after giving birth to her daughter.