Hi there, I will suggest you the best possible treatment options.
First of all do not panic.
Posterior middle segment placenta is not a major concern. Only,
placenta previa , where placenta is located in the lower segment and reaching or covering the internal os, is a major concern. Such situations can cause heavy bleeding even in absence of labour pains and need C section with expert support.
In your case , baby is in vertex presentation, so you can very well undergo trial for
vaginal delivery.
Let your obstetrician be the final authority to decide the mode of delivery.
Things will be fine in the due course of time.
May God bless you with a bundle of Joy.
I hope this answer helps you.
Thanks.
Dr. Purushottam Neurgaonkar