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I don't know the answer to your question, but you should call your OB nurse and talk to her about it, like you are talking about. She should give you advise. If she doesn't, I think I'd find another OB practice...
Regarding neural tube defects, are you taking pregnancy vitamins? One of the best things to prevent neural tube defects, including spina bifida, is folic acid, and it's in pregnancy vitamins. You can go to the pharmacist and talk to him or her about it. The most important time to take them is in the first 8 weeks. It also helps prevents some forms of cleft palate, which developmentally happens at 8 weeks gestation. So, you can see how important it is to get pregnancy vitamins in you ASAP. (Before you conceive is optimal...)