Decline in fetus growth

Was told by my Gyne that there was a decline in baby’s growth (week 36 ultrasound) and showing 34 w 4 days but he is not concerned about it .baby is weighing 2.5kg currently.

I asked him if it’s a matter of concern he said no also he said there is nothing we can do about it as I am small so we cannot expect the baby to be big.

But what I am concern about is what’s the difference between weight and growth he said weight is ok and it is what it should be.

But I am concerned about what he said ghat there was decline in the growth.But baby should gain weight in the coming weeks.

Any gyne ,doctors or OB’s in the group please advice.

Also if someone has similar experience.

Thanks.