Not necessary. Look at Davenport.
I personally think Davenport is the exception though. She is also supported 24/7 by her husband, who travels with her and helps with the baby, which is something Anastasia does not have.
Of course, women can continue to have a successful career after giving birth, but, in my opinion, there's a hell of a lot of difference between returing to the top of a sedentary job or in business (where you can effectively remain working until the last minute), and doing so as a top-class athlete
With the best will in the world, no pregnant woman can train as hard and rigourously as a non-pregnant one, so Anastasia wll lose 6-9 months of training and fitness, during whch time, the other girls will overtake her in rankings, strength and fitness. Add to that the fact that most of the tennis circuit involves non-stop travelling, long-haul flights and changes of routine/Hotels etc, it is not the best start in life for a baby under a year old. Most of the male players I know with families rarely take their partners and babies on tour with them for the first year of a child's life, unless it is a "local" tournament, as the baby needs stability not constant travelling and changes of routine.
I would say she may come back in 2009 to play the odd exhibition and maybe some smaller tournaments, but I don't personally see iher returning to the top echelons of the game, when she will be a single Mother who is not getting any younger (in tennis terms), and younger women with more time to train will be coming up all the time.
I wish her all the best though - as ClayBuzza said, there is more to life then tennis, and giving her baby the best start in life must surely be way more important and fulfilling than the tennis circuit. Good luck to her.