Is 1, 600mcg of folic acid too much during pregnancy?

No, however...: I know of no evidence that this dose would be harmful. The recommended intake for women planning/during pregnancy is 600 mcg. Authorities have set an "upper tolerable limit" of 1000 mcg but this isn't because higher levels are proven dangerous but because it could mask B12 deficiency. However, 30% of people have trouble converting Folic Acid to the active form 5-mthf, so taking that form is optimal.