Does your company have a telecommuting policy? Could you freelance, work part time or jobshare with someone?
A few weeks before my maternity leave ended, I called my boss to ask about the possibility of "alternative work arrangements." There was a seemingly endless moment of silence, and then he burst out laughing. This was probably not a good sign, but I pressed on.
I asked to work from home, and when the company didn't go for that, I asked to go part time. To my great relief, they agreed to a two-and-a-half-day, 20-hour work week. Luckily, many companies today have a variety of options for working mothers.