800 mg. If your pregnant 800 to 1000mg of Folic Acid per day will suffice to help with growth and many metabolic processes for both you and baby. More so having adequate Folic Acid levels before conception (400mg/day) can reduce some birth defects of the heart and nervous system. So it's never to early to start (folate (folic acid) is a water soluble b vitamin so excess is excreted in urine).
0.4-0.8 mg. Generally speaking 0.4-0.8 mg is the recommended daily dose.