It really depends on what ones priorities are. If someone is really in the middle of starting up or even immensely enjoying the current work that she ends up spending most of the time in office, why the hell would you want kids?

Raising decent kids requires proper planning and you need time to observe them and change those plans accordingly if required. Only when you have decided to chill down on work and consider yourself ready for another interesting venture should you go ahead and have kids. Think about your priorities, period.