I did not start taking folic acid until I knew I was 4 weeks pregnant. Now, how much will that affect my baby?

That wont affect your baby at all! most people dont even know theyre pregnant at 4 weeks! So there is nothing for you to worry about

Its nothing to worry about.

that's not necessarily true. that's why doctors recommend taking vitamins and such if you even consider trying to conceive. it depends on the mom... and how her body retains folic acid.. some people don't, or they have a deficiency of it.. and it does affect the baby at conception, just popping pills later won't change an already growing fetus. however its still good to start taking a prenatal and folic acid supplements to help the baby grow (but after conception it won't "prevent" anything)

There is nothing to worry.

its alright to take. safe for the baby