By winning her 23rd Major in January, Williams overtook Steffi Graf's Open era record of 22, but the American remains one Major short of the all-time record 24 held by Margaret Court.
The 23-time grand slam singles champion hinted at a pregnancy when she posted a picture of herself in a yellow swimsuit, showing off a prominent bump, on the social media app Snapchat.
The younger Williams sister is just one Grand Slam short of Margaret Court, who collected many of hers in an era when the difficulties of global travel often diluted the fields.
World number two Serena Williams is expected to return to the top of the WTA rankings next Monday as two-time Grand Slam champion Angelique Kerber's points of winning the Porsche Tennis Grand Prix in her home country of Stuttgart, are expected to come off. Her only other tournament this year was in Auckland, New Zealand, where she lost in the round of 16. Serena's knee injury in March caused her withdrawal from the BNP Paribas Open in Indian Wells, California. When Clijsters came back, she won three more grand slams and regained the World No. 1 ranking.
She was sidelined for nearly 12 months after her 2010 Wimbledon victory, returning from a potentially life threatening pulmonary embolism.
Williams hasn't played a competitive match since she beat her sister Venus to win the Australian Open.
This will be her first child with fiancé and co-founder of Reddit, Alexis Ohanian. She won it again the next year, followed by the Australian Open title, making her the first mother to win a Major since Evonne Cawley in 1980.
If Williams does return though, there's a blueprint for her post-baby comeback.
Victoria Azarenka of Belarus was one of the game's top threats when she left last year to have her first child and the 27-year-old will have one of her main obstacles removed when she returns to competition later in 2017.
That was less than five months ago so we must assume that Williams knew she was pregnant at the time of her engagement announcement.
Ohanian is the latest in a long line of suitors for Serena - she has also dated filmmaker Brett Ratner, basketball player Amar'e Stoudemire, and rapper Common. "I look forward to being back as soon as I can".
Williams, who is 5 feet 9 inches (1.75 meters) and weighed 155 pounds (70 kg) according to her tennis association profile, won a 23rd Grand Slam tournament title at the Australian Open in January.