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
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