Didn't take prenatal vitamin consistently while trying to conceive.?

I did not take my prenatal vitamin consistently before I found out I was pregnant. I knew before my period was due that I was preg (BFP) and started taking it immediately and have every since. I don't eat the worst but I know they stress the importance of making sure you take the vitamin while trying to conceive. I just had my second trimester test done today (wont know results for 5-7 days) and I'm wondering if not taking the prenatal will increase my chances of having a neural tube problem...spina bifida, etc.