You did well in enquiring. Even with the healthiest, well designed , revised by a dietician diet, you need to supplement.
I bought a zillion books, use nutritional analysis websites to monitor all my macro and micro nutrients, have regular blood test, and was severely malnourished, dangerously so when it comes to omega 3 (and by the way, you also need EPA , not only DHA).
You see, the micronutrients in a food on paper , be it a vitamin or a mineral , doesn't always translate into your body being able to extrapolate that mineral or vitamin and storing it.
On paper , I was eating more than 800% of ALA - the plant omega 3- which " should" be converted by the body into EPA and DHA. The conversion is inefficient so you need more. Turns out, my body converts a big 0, and I was so low on omega 3, I had cognitive issues.
At first , when I became vegan, I was only taking B12, now I have a full cabinet of supplements, which I have added one by one, one blood test after the other. Sometimes, when I open that door, I think how can this be healthy.
I have a genetic condition which I try to control by diet and this is why I became vegan, to turn the fate and control specific cellular growth pathway, so I really have done my homework with books, and even online courses on nutrition , and my personal experience, is that one MUST supplementing with a vegan diet.
The what, how much and when is not something you should ask solely on a social forum @blackkitty1234 , you should have at least one consolation with a dietician .
A food is not only made of vitamins and minerals. It affects hormones and gut microbiome. You are building your own microbiome now which you will transmit to your child during birth. What you are eating now, will affect the species, and even without going into such tiny details, what you are eating now, will affect your child's food preferences, and of course diet in the womb is key to optimal development.
www.ncbi.nlm.nih.gov/pmc/articles/PMC4924183/ and this one on pregnancy only which you should read.
www.ncbi.nlm.nih.gov/pmc/articles/PMC6470702/
You care which is what any mother would do, so focus on your baby's wellbeing which can't come from a bottle of supplements alone.
Talk with your partner about making the changes as a growing family.
When a baby is born, a chapter closes - the carefree world of a couple - and a new one opens - being responsible for the health and care of a new being. In your case, this new chapter should start now.