One source of information that I know of is Breastfeeding and Natural Child Spacing by Sheila Kippley (available from LLL) LLL also has another book called Your Fertility Signals- Using them to achieve or avoid pregnancy naturally by Merryl Winstein. There is also a pamphlet called Guidelines Breastfeeding, Family Planning, and the Lactational Amenhorrhea Method- LAM by Mirriam Labbok, Kristin Cooney, and Shirley Coly Published by the Institute for Reproductive Health Georgetown University Department of Obstetrics I have parts of the Labbok article from the CERP book at the LLLI conference last July. It has references and is concise and clearly written. Hope this helps. Sarah Friend Barnett, LLLL, IBCLC Bronx (New York City), New York [log in to unmask]