Is anyone else strugling with the decision of having more children or go forward in their career?

I'm almost 30and would love another child next year,But I know it will affect my career badly. I have always worked and would carry on working ,but I graduated last year and my job prospects are about to change . I'm struggling to make a decision, should I trow myself at the new job and risk waiting 5 or 6 years or should I delay this opportunity and have another child now and career later. i already have a 9 year old but would hate for him to be a single child