Pregnancy blood draw ?!

I don’t get why obgyns don’t do the pregnancy blood tests right away because apparently low vit d can cause a miscarriage which I’m known for having low vit D but my doc just doesn’t care ? What if I’m low in a bunch of vitamins by the time they find out at 10 weeks my baby will either have a bunch of development problems from it or I’ll have a miscarriage ?? I’m really scared rightnow