Serena Williams has revealed how she almost died giving birth to daughter Alexis Olympia Ohanian Jr in September.

The former world number one gave details of her harrowing experience in a column for CNN that was published on Tuesday.

In the piece, the 23-time Grand Slam winner said that giving birth had led to a number of serious health complications.

“I almost died after giving birth to my daughter, Olympia,”the 26 year old Williams,  wrote.

“My daughter was born by emergency C-section after her heart rate dropped dramatically during contractions. The surgery went smoothly.

“But what followed just 24 hours after giving birth were six days of uncertainty.”

Williams then went on to talk about the problems she had suffered post-birth: “It began with a pulmonary embolism, which is a condition in which one or more arteries in the lungs becomes blocked by a blood clot.

“Because of my medical history with this problem, I live in fear of this situation. So, when I fell short of breath, I didn’t wait a second to alert the nurses.

“First my C-section wound popped open due to the intense coughing I endured as a result of the embolism. I returned to surgery, where the doctors found a large haematoma, a swelling of clotted blood, in my abdomen.

“When I finally made it home to my family, I had to spend the first six weeks of motherhood in bed.”

Williams has previously said she had been bedridden for six weeks following the birth, but had not provided details until now.

She went on thank the medical team for helping to save her life before talking about child-related deaths among black women in the US and around the world.

Williams raised a few eyebrows last year when she won the Australian Open, her 23rd Grand Slam title, while eight weeks pregnant.

The American is now just one grand slam title short of Margaret Court’s all-time record.

She missed this year’s Australian Open as she was still recovering from the birth, but made a return to competitive tennis earlier this month at the Fed Cup.