Your best bet is to go ahead and start taking a prenatal vitamin now. They contain more than enough folic acid for you and doctors actually recommend for women who are trying to conceive to take them.
Here is a diret quote from one site:
(TTC= trying to conceive)
It does not have to be prescription prenatal vitamins. An over-the-counter multivitamin with 400 mcg folic acid and no megadoses of other vitamins is recommended in women TTC. Folic acid is crucial to prevent neural tube defects in the developing embryo. The neural tube is formed at a time when most women do not even realize they are pregnant, so it is a good idea to be taking supplements as soon as possible, preferably beginning up to 3 months before TTC.
Good luck and happy baby making!

Hi,
Actually there are 3 brands in Prenatal vitamin tablets.
Can you suggest a good one?

If any of them has a name that has been around a while or is well known, it should be fine. Offhand, I don't know of any brands that are preferable. What I do know is this: you should not buy cheap vitamins. While they may contain the same percentage of a vitamin, they do not have the proper coating. The more expensive brands will be absorbed into the body while you will only get a fraction of the cheaper version; the rest will literally be flushed down the toilet as waste.