Neural tube defects

Lacey • I am 33. Married for Eight years. I am a dental hygienist. My husband works in industrial mechanics. We have a 2 year old little girl and are trying for baby #2
I didn't know I was pregnant until 5 weeks. I was not taking prenatal vitamins because we didn't think we were going to be able to have children. I'm really worried about our baby girl having a birth defect, should I be worried? I have my anatomy sonogram on Wednesday. I am 17w.