DHA and prenatal vitamin

L
When I called my doctors office  I scheduale my first appointment they sent in my prescription for prenatal vitamins but also told me I need to take DHA, I don't remember taking it when I was pregnant with my son though, that was almost 4 years ago so maybe I just forgot? Anyone have any information or input on this subject? Anything would be helpful, I'm 7 weeks today, my first appointment isn't until January 20th.