Once again, Serena Williams is a woman apart - she must be the only new mother returning to competition whose husband designed and paid for roadside billboards, describing her as 'The Greatest Momma of All Time'. 

And Williams' story is a uniquely alarming one; she wrote in a story for CNN how she "almost died" after giving birth because of "a slew of health complications", and she spent the first six weeks of motherhood in bed. And yet, in other ways, Williams has much in common with Kim Clijsters, Victoria Azarenka and other WTA mothers going back to work. Physically, there is no greater challenge for a professional tennis player than aspiring to compete again after childbirth. And not just to compete, but to go back to winning titles again. 

Patience is required when you're starting from near-zero

In Azarenka's experience, any new mother hoping to regain her fitness "is starting a little bit from zero", she told the media during last year's Wimbledon Championships. The first few occasions that Clijsters spent time on the practice court after becoming a mother, she struggled with her movement. "Your body just feels so different. I had a good feeling when the ball was coming towards me, but just moving was absolutely terrible," she told the press during the 2009 US Open. "I felt like an elephant sometimes, just trying to move." 

An opportunity to be fitter than ever before 

As she prepared for her comeback, Clijsters had the chance to "work on weaknesses and those little injuries" that previously she had not the time to address because of her busy tournament schedule. On her return, she was perhaps stronger and fitter than she had been before, and could also still do the splits; she would win three Grand Slam titles as a mother, having scored one during her 'first' career. When Azarenka played at last summer's Wimbledon, she felt as though she had improved her physical conditioning when training for her return, and said during one media conference: "I definitely feel fitter than I ever have been before." 

Kim Clijsters says she struggled with her movement in the immediate return from her pregnancy (Getty)

The core is the key

Regaining the strength in her core was fundamental to becoming a force in tennis again, says Clijsters. "After my pregnancy, I had to get my core back in shape. I think that was tough because I had been playing tennis since I was five years old so my core, my lower back, that was always something that was very strong. But after the pregnancy, that just goes," the Belgian said in 2009. "So you have to re-teach all those muscles to contract when they're supposed to with each shot you hit. You have to remind your muscles to move at that time. They're the most boring exercises ever, but I felt as though that was something I had to do." 

Victoria Azarenka 'felt fitter than ever before' after returning to the game (Getty)

A comeback in stages

Williams' own fitness trainer, Mackie Shilstone, has spoken of how he planned to start by "re-establishing her female physiology", by which he meant addressing the cardiovascular and metabolic changes in her body during the pregnancy. Then he would "establish her baseline fitness", according to an interview in The Guardian last April, before turning to her fine motor skills.  

Nothing is impossible if you love what you do
"If you're passionate about what you do, and you love what you do, then you [get your fitness back],” Azarenka told a press conference. "The guys have the luxury of never stopping their careers, and for the girls it's tougher. But I think it's possible. Even before, you had players doing this, with Kim Clijsters and also a lot of other girls who were lower-ranked so their stories aren't as big. It's possible. Nothing is impossible. For women, that's definitely true."