400 or 1,000 mcg of folic acid ??

I hope some of you are up... I've been taking 400mcg of folic acid (it's inside my vitamins flintstone complete) but I just checked the folic acid amount in the prenatal vitamins my OB prescribed me and its 1,000 mcg. I am confused on the big difference and not sure which amount I should be taking. I am 107lbs and 13 weeks pregnant. Help? Anyone ?