3 miscarriages and a&c mthfr should I be on lovenox (enoxaparin) or heparin on next pregnancy?

Discuss with doctor. Not sure what a&c means. Mthfr mutation is very weakly associated with miscarriage. If you are heterozygous then blood thinning medicines are not indicated. If you are homozygous then possibly. Ask about a fasting homocystine test. Your age of 41 is also a risk factor for miscarriage.
Discuss with a . Hematologist about a blood disorder possibly causing your miscarriages. Best wishes !