21 yr old pregnant patient with sickle cell disease, 2 strokes, now on exchange transfusions in 3rd trimester.

I have been following a wonderful young woman since she was 16-years-old. She has sickle cell disease and had 2 strokes the last being in 2006. She was treated with simple transfusion protocol; however, IV access became a problem. We placed a pheresis port and she has been successfully exchanged by Red Cross every three weeks with no complications. She graduated from college and because we could not find another center to continue the pheresis in Charlotte, she stayed in our clinic and is working to complete her Masters in Social Work.  Ferritin is 1500. She is now 26 weeks pregnant. I have been trying to find any experience of continued exchange transfusions through third trimester without much luck. In addition, we performed a thrombophilia evaluation last week. Patient is heterozygous for Factor V Leiden with Protein S of 24%. Factor 8-199% and Factor 5-174%. Homocysteine level is normal and no prothrombin mutation.So far, the baby is doing well and our patient is doing well. She is followed by Maternal Fetal at Novant Health Presbyterian Main Hospital in Charlotte. My plan is to continue exchange transfusions until delivery to maintain S below 30%. Concern for prethrombotic environment with the viscosity of simple transfusions may compromise placental perfusion. With the new findings of heterozygous Factor V Leiden and Protein S, and a history of presumed sickle cell related strokes, would the experts recommend additional treatment: Low dose heparin, Lovenox, etc.? Do they agree with the continued pheresis? Yes or No, and why? Thank you so much, and I would be glad to add any additional information they may need.