CBS12 reporter Thomas Forester confirmed Williams checked into the hospital Wednesday and has the entire first floor cleared, no one can get in without going through security.
The Palm Beach Gardens resident is engaged to Reddit co-founder Alexis Ohanian, 33. This is their first child.
The 23-time major winner has said she hopes to return to the game in time for the Australian Open in January.
Serena won her record 23rd Grand Slam title at this year’s Australian Open over her sister Venus.
The 35 year-old has not played since early this year.
But, she has posted several videos on social media showing her hitting during her pregnancy.