Son with suspected constitutional growth delay

My son is nearly 4 and has recently undergone tests regarding his growth. All bloods came back ok but they did a scan of his wrist and is bone age was 2 to 2 years and 8 months. They have said that it is constitutional growth delay. My son is only on 0.4th percentile for height and 2nd for weight. Is this normal even in constitutiional growth delay for him to be so tiny? What would his adult height likely to be like? As he is so small may he need growth hormones? I have asked to be referred to an endocrinologist just to confirm this diagnosis. As a baby he was born at a normal weight and height but then his growth slowed. We just assumed that it was because my husband and I are small, I'm 5'5 and husband is 5'7. Even the health professionals were not concerned initially, it was only after I insisted he was unusually small that they referred me to a paediatrician.