The after coming head of the baby in a breech delivery can be arrested by all of the following except:
If a whole baby can make its way from breech onwards till the head, then even if there is a placenta pre, it will not obstruct the fetal head to come though since there was no obstruction to the whole fetus.
Extended head
Hydrocephalus
Placenta pre
Incomplete dilatation of the cervix
Labour - II