Are you talking about MTHFR genetic defects? These have to do with how your body process vitamin B12, B6 and folic acid. Folks with more severe defects will often have elevated homocysteine. I'm am heterozygous for the C677T mutation, which means that I have low levels of the enzymes that allow your body to effectively utilize the B-12/folic acid and B6, so you I need to take extra B-12 sublingually or through shots, along with folic acid and B6. I did not have elevated homocysteine, but I had tremendously elevate folate because my body couldn't properly use in the methylation cycle. If you're homozygous for that particular defect, then it's more of an issue. You should ask your doctor about this and what exactly you should do. But before you get too worried, 40% of the population is heterozygous for this particular defect that I have. Here's a link on this topic and pregnancy:
I did not find out about this issue until after I had given birth to my two boys, so I don't think the heterozygous has a huge impact on pregnancy, but I do know the homozygous might. But, again, you should really talk to your doctor about this and whether you need the B-12 shots or at least additional supplements.