LOS ANGELES • Serena Williams may be fearless from the baseline but off the tennis court, the former world No. 1 remains haunted by the medical condition known as blood clots.

In an op-ed piece she wrote for CNN on Tuesday, the American lifted the lid on her near-death experience while giving birth to daughter Olympia in September, after getting blood clots in her lungs.

"I almost died after giving birth to my daughter," Williams said.

The 23-time Grand Slam champion said she had to have an emergency caesarean operation after her heart rate plummeted dramatically during contractions.

In a Vogue magazine interview in January, Williams said that during her post-natal ordeal, she suffered a pulmonary embolism - when blood clots block arteries in the lungs.

And that was not the first time the 36-year-old has had a scrape with death from blood clots.

In 2011, she spent nearly 12 months incapacitated after a cut on her foot from a piece of broken glass led to a pulmonary embolism. "Because of my medical history with this problem, I live in fear of this situation," she said.

Williams added that one day after the surgery, she felt short of breath and was put her on a drip.

But her ordeal was not over.

She started coughing so much from the blood clots that her wound popped open.

"Doctors found a large haematoma in my abdomen. I returned for a procedure that prevents clots from travelling to my lungs. I had to spend six weeks of motherhood in bed."

Williams praised the hospital staff, saying: "If it weren't for their professional care, I wouldn't be here today."

She made her long-awaited comeback this month, playing for the United States alongside her sister Venus in a Fed Cup doubles loss to the Dutch pair of Lesley Kerkhove and Demi Schuurs, as the team won 3-1.

THE GUARDIAN