DHA + iron during pregnancy

I will be starting ttc next month and have purchased my first bottle of prenatals. It’s the first response brand. I read about these gummies not having dha and iron, so I’m wondering if I have to get those individually right now or only after conceiving? Could someone also explain why you need dha and iron during pregnancy, I was only ever told about folic acid by my doctor. Thank you in advance 💞☺️