I don't know anything about pregnancy during the postpartum timeframe, as I have always breastfed and have never gotten my period back before 1 year. With the twins, it was 20 months before getting it back..... I was worried that I was going into menopause at age 34!
I was also diagnosed with MTHFR after having a preterm baby and two pregnancy losses. They didn't have a test for it back during my first pregnancy, but did after I suffered the two losses. I was told that I needed to take the extra folic acid, vitamin B-6, and baby aspirin for the rest of my life, regardless of whether I was pregnant at the time. This is to prevent any microscopic blood clots that could affect me, not just the ones that could develop in the placenta during a pregnancy. You might want to ask your doctor about this, and if you find out anything to the contrary, please let me know too.
Thanks, and good luck!