Timing is everything.

For the organising committee of Glasgow 2014, Jessica Ennis' announcement yesterday that she is pregnant and will therefore miss the Commonwealth Games is far from ideal, but for Ennis herself, the timing is almost perfect. The 27-year-old was the star of London Olympic - winning heptathlon gold gloriously on Super Saturday, while carrying the hopes of the nation on her shoulders - and having a child this year allows her to set her sights on defending her Olympic title in 2016.

In a statement, Ennis, who married her long-term boyfriend last year, said that she aims to return to athletics after giving birth. "My plans for 2014 have been completely turned upside down but, having had a couple of weeks to think about things from a career point of view, I am 100% set on returning to full-time athletics once our baby is born and go for a second gold medal at the Rio Olympics," she said. "That challenge really excites me, but in the short-term, I will make our baby a priority and enjoy the whole experience as much as possible."

Ennis added that she is disappointed she will not compete at Glasgow 2014 this summer but that the timing of her pregnancy, in theory at least, allows her the opportunity to defend her Olympic title will come as a relief. Ennis will have two years between the birth of her baby and the start of the 2016 Olympics which - if there are no complications - should give her sufficient time to return to an elite level.

Judging by history, Ennis' ambitions are not unrealistic. Numerous female athletes have returned to elite sport after having a baby; some have even surpassed their previous performances on their return. Tennis player Kim Clijsters' achievements following the birth of her daughter significantly overshadowed everything she had accomplished previously. The Belgian won the US Open in 2009 in just her third tournament after returning to action, repeated the feat the following year and then won the Australian Open before retiring.

In athletics, comebacks after having a baby are relatively common. Liz McColgan famously ran right up until the day she gave birth and was back training just 11 days afterwards. She won World Cross Country bronze less than four months after becoming a mother in 1990 and became 10,000 metre world champion in Tokyo the following year.

There are many other examples of women achieving success after childbirth. Distance runners Paula Radcliff and Sonia O'Sullivan both rescaled the heights they previously had reached, American cyclist Kristin Armstrong won Olympic time-trial gold in 2012 and her compatriot, Dara Torres, won multiple Olympic medals in swimming in 2008.

While returning to elite sport as a mother is far from easy, there is evidence to suggest that pregnancy can provide a boost to performance. Pregnancy results in increases in blood-flow and oxygen-carrying capacity, mimicking the benefits of blood-doping, as well as increased levels of growth hormones. Studies show that most of the physiological benefits disappear six to 12 months after pregnancy but some hormonal changes can be long-lasting.

The performance benefits of a pregnancy were so strongly believed in the late 1980s that there were copious rumours of "abortion doping". Allegations abound that doctors were inducing pregnancies in Eastern European athletes and then aborting the baby in order for the female to benefit from the hormonal changes.

There is, however, little concrete evidence to support the claim that pregnancy improves performance, due to the limited opportunities to carry out studies. For Ennis, her future remains unclear. However, if she returns to full health and her motivation is restored after the birth of her child then there appears little reason why she cannot retain her Olympic title in Rio in two years' time.