In a Vogue cover story released Wednesday, Serena Williams revealed she had a terrifying health scare after giving birth to her daughter Olympia in September which hospital workers initially ignored.

After her heart rate took a dip during labor, Williams said she had an emergency C-section. Fortunately, the surgery went smoothly, and Olympia even stopped crying the moment she was laid down atop her mother.

“That was an amazing feeling,” Williams told Vogue. “And then everything went bad.”

The next day, Williams said she felt short of breath and grew concerned she might be having a pulmonary embolism. Williams said she regularly takes blood thinners due to her history of blood clots, one of which she nearly died from in 2011.

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Williams said she told a nurse she needed a CT scan and a blood thinner immediately, but the nurse thought the pain medicine had left her confused. When Williams further insisted on treatment, a doctor instead performed an ultrasound of her legs. “I was like, a Doppler? I told you, I need a CT scan and a heparin drip,” Williams said she told the medical team.

The hospital workers performed a CT scan after the ultrasound revealed nothing. Indeed, they found several small blood clots in her lungs and treated her with blood thinners.

Williams’ harrowing childbirth story has ignited a conversation about the high rates of maternal mortality and birth complications in the United States, which black women face at an alarmingly disproportionate rate.

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About 700 women in the United States die each year as a result of pregnancy or delivery complications, according to the CDC. And, according to a recent report by ProPublica, black women are three or four times more likely than white women to die during childbirth. People are pointing out that, despite her wealth and fame, Williams still had to self-diagnose.