Speech delay in preemie toddler

Has any other parents experience a speech delay with their prem toddlers? My son is 2 and still only babbles does not speak. We have been referred to SLT and had his ears checked already. He babbles yeah and dada quite a lot, he has good understanding and imagines play quite a lot. But just won’t copy our words or try to speak. He loves reading too but just looking for advice or reassurance really! He was 6 weeks early with IUGR due to pre eclampsia, could this be a factor?