Serena Williams insisted here on Sunday that she had no problem whatsoever being drug-tested but queried why she had been targeted five times already this year by the US Anti-Doping Agency (Usada).

The seven-times Wimbledon champion, who has played only seven matches since returning to competition after a 14-month break to have her first baby, said she wanted to ensure fairness towards all players in drug-testing procedures.

Williams was surprised when a drug-tester recently turned up at her Florida home at 8.30am, which was outside the time she had told the authorities that she would be available to be tested each day. She was not at home at the time, but the Usada drug-tester refused to leave.

8 of the most controversial Wimbledon outfits of all time Show all 8 1 /8 8 of the most controversial Wimbledon outfits of all time 8 of the most controversial Wimbledon outfits of all time In 1985, Anne White wore an all-white catsuit while competing at Wimbledon. Her opponent, Pam Shriver, complained to officials about her choice of attire. Getty Images 8 of the most controversial Wimbledon outfits of all time In 1949, Gertude Moran, commonly referred to as 'Gussy', caused quite a stir at the tournament when her lace undergarment was spotted during gameplay. Getty Images 8 of the most controversial Wimbledon outfits of all time In 1987, Pat Cash bent the Wimbledon dress code rules by wearing a black and white bandana, despite rules stipulating that accessories should be predominantly white. Cash ended up beating Ivan Lendl in the final to take home the men's singles trophy. Getty Images 8 of the most controversial Wimbledon outfits of all time Following his win at the 2009 Wimbledon's men's singles final against Andy Roddick, Roger Federer donned a jacket embroidered with the number 15, in celebration of his 15th Grand Slam win. Some found the fact that the jacket had been made prior to the match presumptuous. Getty Images 8 of the most controversial Wimbledon outfits of all time In 2017, Venus Williams was reportedly forced to change her bra midway through a match when her pink straps became visible. Getty Images 8 of the most controversial Wimbledon outfits of all time In 2007, Tatiana Golovin became a much-discussed topic of conversation due to the red shorts that she decided to wear while competing. Rex Features 8 of the most controversial Wimbledon outfits of all time In 2008, Maria Sharapova appeared to poke fun at the strict dress code imposed by Wimbledon by wearing a tux-esque outfit. Getty Images 8 of the most controversial Wimbledon outfits of all time In 1977, Sue Barker, who will be hosting live coverage of Wimbledon this year, was criticised for her 'risqué' hemlines at the competition. Getty Images

The Deadspin website reported that Williams had been drug-tested five times this year by Usada while other American women players had been tested no more than twice. Williams, who was reported to have complained to Steve Simon, head of the Women's Tennis Association, said on Sunday that her experience had been “shocking”.

The 36-year-old American said that she had sat on the WTA’s player council for 12 years and was therefore well aware of drug-testing rules. She said her understanding was that as the world No 1 she would have been liable to frequent drugs tests, but was puzzled by the number she was continuing to undergo after being out of competition for more than a year. She is now ranked No 181 in the world.

“How is it I'm getting tested five times?” Williams said. “I’m OK with that. Literally verbatim I said: ‘I'm going with that, as long as everyone is being treated equally. That's all I care about.’

“I despise having people in our sport that aren't being honest. I'm totally OK with testing and I encourage it. I'm OK for it. What I want to know is everyone is getting tested, that we are really working to keep this sport clean.

Serena Williams queried why she had been subjected to more drug testing than her opponents this year (Reuters)

“Tennis has given me so much. It's such an amazing sport. I feel like equality, that's all I've been preaching, it's all about equality. If that's testing everyone five times, let's do it. Let's be a part of it. It's just about being equal and not centring one person out. Just due to the numbers, it looks like I'm being pushed out. Just test everyone equally.”

Williams said the experience of the drug-tester turning up at her home outside her “whereabouts” window had been frustrating.

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“Every day, every player gives a time for testing,” she said. “My time was actually 12 hours later. For some reason they showed up in the morning, which they are allowed to do. And if I'm not there, then [normally] they just leave.

“For whatever reason they didn't leave. They said I can come back. I was like: ‘I'm totally not in the area because my hour is actually a long time from now. I'm completely so far away’.”

She added: “It’s really disappointing, shocking. I was just like: ‘That's just weird.’ I'm still trying to figure out why and how that happened.”

Serena Williams returns to Wimbledon this week after missing 2017 (Reuters)

Williams was also asked at her pre-Wimbledon press conference how difficult it had been deciding to stop breast-feeding her daughter, Olympia, who was born in September.

“I had planned on stopping in January,” she said. “Then January became March. March became April. I was still breast-feeding. For me, it was really important to make it through three months, then it was important to make it to four months. I was like: ‘OK, I can do six months.’ I was training and everything.”

Williams said she had been told to expect that she would lose weight while breast-feeding but it had not happened, despite the fact that she had been following a vegan diet and was eating healthily.

She explained: “What I've learned through the experience is that every person is different, every physical body is different. For my body it didn't work. No matter how much I worked out, no matter how much I did, it didn't work for me.

“Once I got to six months, I felt good about it. Then it was just emotionally letting go. That was a different thing. I literally sat Olympia in my arms, I talked to her, we prayed about it.

“I told her: ‘Look, I'm going to stop. Mommy has to do this.’ I cried a little bit, not as much as I thought I was. She was fine. She was totally fine. It was the strangest thing. I just learned from that experience that every physical body is different.