Williams made her 10th Wimbledon final in July 2018, her first Grand Slam final appearance since giving birth to Olympia in September.
The American lost 3-6, 3-6 against Angelique Kerber in the championship match, attempting to equal Margaret Court's 24 Grand Slam titles.
During her grasscourt Major campaign, Williams complained about being tested more than her American peers.
After her Wimbledon final loss, Serena Williams joked on social media about the apparent gap in random drug testing between her and other competitors, indicating it was discrimination.
Although frustrated at being singled out for drug tests, the former World No. 1 stressed her devotion to sport purity.
"I'll do anything to have a clean sport, so bring it. I'm thrilled "she added. Two months before, she said she was tested "two times every week" despite being World No. 454 at the time.
Anti-doping is back again this week. Participating to clean the sport makes me proud.
Even if they test me at 454th in the world. Two times a week #BeingSerena "posted.