What Causes Elevated Platelet Count In Blood During Pregnancy?

Hello, I am 35yrs old and I am 27 weeks pregnant with my 3rd child. I am concerned because my platelet count is high. should I be worried? I am O neg RH Neg could this have something to do with it. I was told I am Anemic on my last visit as well. What would make my platelet count high? Please advise. Thanks