There aren't a lot of new books on miscarriage out there but I did find an older book (2001) which I love. The book isn't specifically about miscarriage but I think it would be very helpful if you wanted to help someone who had a miscarriage.
The book is called “Healing a Friend's Grieving Heart; 100 Practical ideas for Helping Someone You Love Through Loss.” It was written by Alan D. Wolfelt, PH.D.
The first thing that's great, is that it's a fairly short book. I'm certainly not opposed to long books but sometimes it can be difficult to offer advice in the form of a book which will take the reader a long time to finish. Additionally, the book is set up so that you can leaf through it and begin reading anywhere.
Dr. Wolfelt has included one idea on each page. He offers a few brief paragraphs explaining each idea, then offers a short way in which you could implement each idea. For example, idea number 31 is “Be Mindful of Anniversaries”. He explains why anniversaries can be difficult for a grieving person. Then he suggests writing anniversaries on your calendar (including anniversaries of death) so that you know which days may be most difficult for your friend. Transferring his advice to miscarriage, someone might be upset not only by the anniversary of the miscarriage itself but perhaps the day she found out she was pregnant as well.
Other ideas include information on planning ceremonies, things to say to a grieving friend (as well as things not to say), advice about self care and ways you can help a grieving friend get out and have fun.
Dr. Wolfelt also has a website www.centerforloss.com. The website has many valuable resources as well. The website's bookstore includes books on healing other forms of grief including a book on healing after stillbirth and healing after the loss of a child.
If you've had a miscarriage or want to support someone who has had one, I would definitely recommend checking out this book and website as well.