Serena Williams has revealed she ''almost died'' after giving birth to her daughter last year.

The 36-year-old professional tennis star previously admitted had to undergo an emergency c-section when she gave birth to daughter Alexis Olympia - whom she has with her husband Alexis Ohanian - in September last year, but she has now revealed the situation was so dire she almost lost her life just days after giving birth.

She said: ''I almost died after giving birth to my daughter, Olympia. Yet I consider myself fortunate. While I had a pretty easy pregnancy, my daughter was born by emergency C-section after her heart rate dropped dramatically during contractions. The surgery went smoothly. Before I knew it, Olympia was in my arms. It was the most amazing feeling I've ever experienced in my life. But what followed just 24 hours after giving birth were six days of uncertainty.''

Serena admitted she was plagued by health problems after giving birth including a pulmonary embolism, which is when a blood clot forms in one or more of the arteries in her lungs.

She continued: ''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.

''This sparked a slew of health complications that I am lucky to have survived. 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 hematoma, a swelling of clotted blood, in my abdomen. And then I returned to the operating room for a procedure that prevents clots from traveling to my lungs. When I finally made it home to my family, I had to spend the first six weeks of motherhood in bed.''

The tennis superstar then thanked her ''incredible medical team'' for saving her life.

In a piece written for CNN, Serena said: ''I am so grateful I had access to such an incredible medical team of doctors and nurses at a hospital with state-of-the-art equipment. They knew exactly how to handle this complicated turn of events. If it weren't for their professional care, I wouldn't be here today.''