I think that you are not considered a grand multip (ie someone who is high risk because of the number of times they have given birth) until you have had 5 children. However with each CS your risks tend to raise so I imagine they would be keeping quite a close eye on you to make sure that your scar and placenta are doing what they are supposed to. I would imagine they would prefer you to receive your care at the larger hospital as a result of this, but the best person to ask is your midwife or OB who can let you know local policies.