Post Pigmentation after Fractional (Photo)

Hi everyone, I am 31 years olf female Asian with fair skin. I have old white strech marks on my abdomen. I have done some Fractional Laser on my tummy. Just want to ask is it normal to have Post Pigmentation after 1 session? I plan on doing then for 6 to 8 session every 4 weeks. My doctor's advise said that Post Pigmentation is normal after procedure. Just want to ask your opinion as other derm clinic I didn't experience this.