Baby undersized 25 weeks

ok my friend is preg.. with her 1st baby, shes in her 25week yesterday she was bleeding really heavy, so we ended up going to the hospital, there they took some test and did ultrasound and told her that her baby is not growing, the size of her baby is only 7.83 inches, but it should have been 13.62 inches they told her if her baby doesn't reach 9.84 inches by end of her due date her baby might not survive. so my question is what could have gone wrong with her pregnancy???
could it be because her husband had Hep C and in her blood test they told her that she had blood cancer signs, but after they took 2nd blood test there were no signs of blood cancer.