Former world number one Serena Williams said she almost died giving birth to daughter Alexis Olympia Ohanian Jr in September.
The American, 36, made her competitive return earlier in February when she teamed up with sister Venus for the United States in the Fed Cup.
But the 23-time Grand Slam winner has revealed that giving birth "sparked a slew of health complications".
"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.