hlm, tests of nutrient status are a very smart idea (i'm not biased lol)
several of the b complex vitamins are known to be low in ms cases - b12 is just the 'flagship' as it were. they're also important in pregnancy.
if you want to just try something out, a b-50 complex is a good starting point. the amounts are safe for long term use, but if you try it for say 3 weeks to see if you notice a difference, it could help. you probably already know that b9 is always recommended to expecting mothers.
if you decide to start the b50 without a test first, just keep your doctor in the loop in case he or she wants to do some bloodwork.
b1 thiamine - requirements much higher in pregnancy
During pregnancy, approximately 50% of the women develop a biochemical thiamine deficiency, whereas the thiamine status falls, but remains within normal limits, in most other women
b2 riboflavin, b3 niacin (nicotinamide)
Maternal intake of fat, riboflavin and nicotinamide and the risk of having offspring with congenital heart defects.
A maternal diet high in saturated fats and low in riboflavin and nicotinamide seems to contribute to CHD risk...
the choline in b-complex is another important factor, along with b9 folic acid, in preventing neural tube defects.
Choline and Risk of Neural Tube Defects in a Folate-Fortified Population.
that's all for now,