I would recommend going to the Association of Women's Health, Obstetric and Neonatal Nurses (AWHONN)
www.awhonn.org They have a resource for sale that discusses that issue.
If you want something quicker, I'd suggest looking in the Journal of Obstetric, Gynecologic and Neonatal Nursing (JOGNN) at a local health science library, or doing a literature search to obtain that information.