The baby is small (AC less than 10th centile is generally speaking smaller than what would be expected at that stage in pregnancy).
The umbilical artery doppler being normal means that there is sufficient blood flow to the baby from th placenta, to keep it alive. But as baby is small, it is probably not receiving enough blood to maintain normal growth.
The MCA Doppler is a way of assessing the blood flow in the baby's brain. This seems to have been affected, as a PI of < 5th centile is abnormal.
The biophysical profile is an assessment of baby's activities in the womb, which is still being maintained normally at 8/8, which is reassuring.
We have to take all the parameters into account, when deciding time of delivery. Your baby is preterm as well, and will need additional help and support as there are risks from prematurity.
You should keep a close watch on baby's movements, and inform your obstetrician if there are less movements.
You will also need daily fetal monitoring with CTG (ie pattern of baby's heart rate plotted on a graph for at least 40 mts)
You will need umbilical artery dopplers at least twice a week.
Any deterioration in any of the above mentioned, will need an early delivery. Otherwise it may be possible to carry on for a week or more, but it is unlikely that you can go to full term without compromising your baby. If you can get a few more weeks, that will help the baby to mature a bit more, as every week counts.
If you are delivered early, you will need two injections of dexamethasone or betamethamethasone, 12 or 24 hours apart, to help baby's lungs to mature.
You should also consider delivery at a centre with good neonatal intensive care unit.
Hope all this information helps. Please see a good obstetrician or fetal medicine specialist for treatment and care.