Serena Williams won a Grand Slam while eight weeks pregnant

Serena Williams won the 2017 Australian Open — her 23rd Grand Slam singles title, the all-time Open Era record — while eight weeks pregnant, though she didn't know it at the time. The pregnancy was confirmed after her victory. Williams has also returned to professional tennis after a life-threatening pulmonary embolism following the birth of her daughter in 2017, requiring emergency surgery. She has described the combination of pregnancy, near-death medical complications, and competitive return as the most difficult period of her career, and the experience that defines her legacy more than any title.

Source: Williams interview, CNN (2017)