The Book of Common Prayer does not do a good job addressing miscarriages. The older liturgies that I found may have been pastoral in their day but they lack current sensibilities and this is not an occasion to get it wrong.
I found a Roman liturgy that I have heavily redacted and rearranged to follow an Anglican model. The Bishop has given me permission to use it in a hospital setting and so I wanted to share it with my brother clergy and all who minister to those who share this grief.
It can be found in the link below. It prints out well on legal sized paper in booklet form to distribute to participants.