Lactational amenorrhea is the natural postnatal infertility that occurs when a woman is amenorrheic (not menstruating) and fully breastfeeding. If not combined with chemicals or devices, lactational amenorrhea method (LAM) may be considered natural family planning.
Breastfeeding infertility 
For women who meet the criteria (listed below), LAM is 98% - 99.5% effective during the first six months postpartum.
- Breastfeeding must be the infant’s only (or almost only) source of nutrition. Feeding formula, pumping instead of nursing, and feeding solids all reduce the effectiveness of LAM.
- The infant must breastfeed at least every four hours during the day and at least every six hours at night.
- The infant must be less than six months old.
- The mother must not have had a period after 56 days post-partum (when determining fertility, bleeding prior to 56 days post-partum can be ignored).
Ecological breastfeeding 
Ecological breastfeeding is a stricter form of LAM developed by Sheila Kippley, one of the founders of the Couple to Couple League. Studies have shown it has a 1% failure rate in the first six months postpartum, and a 6% failure rate before the woman’s first postpartum menstruation. The Standards of ecological breastfeeding are slightly different from the LAM criteria:
- Breastfeeding must be the infant’s only source of nutrition – no formula, no pumping, and (if the infant is less than six months old) no solids or water at all.
- The infant must be pacified at the breast, not with pacifiers or bottles or by placing a finger in the mouth.
- The infant must be breastfed frequently. The standards for LAM are a bare minimum; greater frequency is better. Sucking should include non-nutritive sucking when the infant cues the mother, not just breastfeeding as a means of nutrition. Scheduling of feedings is incompatible with LAM.
- Mothers must not be separated from their infants. This includes substitutes for mother such as babysitters and even strollers or anything else that comes between mother and physical contact with her child. Babywearing (using cloth carriers) means tactile stimulation between mother and child and increases access to the breast. Any separation from the mother will decrease the efficacy of ecological breast feeding.
- A mother must not have had a period after 56 days post-partum (bleeding prior to 56 days post-partum can be ignored).
The AAP recommends never co-sleeping or bed-sharing with an infant due to the increased risk of smothering and/or SIDS. Although, it bears mention that the AAP definition of co-sleeping is any non-crib surface. However, true co-sleeping simply indicates that child and parent(s) are within the same vicinity (ie baby's crib is placed in parents' room). 
Return of fertility 
Return of menstruation following childbirth varies widely among individuals. A strong relationship has been observed between the amount of suckling and the contraceptive effect, such that the combination of feeding on demand rather than on a schedule and feeding only breast milk rather than supplementing the diet with other foods will greatly extend the period of effective contraception. The closer a woman's behavior is to the Seven Standards of ecological breastfeeding, the later (on average) her cycles will return. Average return of menses for women following all seven criteria is 14 months after childbirth, with some reports being as soon as 2 months while others are as late as 42 months. Couples who desire spacing of 18 to 30 months between children can often achieve this through breastfeeding alone.
Although the first post-partum cycle is sometimes anovulatory (reducing the likelihood of becoming pregnant again before having a post-partum period), subsequent cycles are almost always ovulatory and therefore must be considered fertile. However, some women find that breastfeeding interferes with fertility even after ovulation has resumed. Luteal phases being too short to sustain pregnancy is a common example.
Further reading 
- Kippley, Sheila. The Seven Standards of Ecological Breastfeeding: The Frequency Factor, 2008.
- The Use of Contraception During Lactation - A Fact Sheet - Alberta Medical Association.
- "Comparison of Effectiveness". Planned Parenthood. April 2005. Retrieved 2006-08-12., which cites:
:Hatcher, RA; Trussel J, Stewart F, et al. (2000). Contraceptive Technology (18th ed.). New York: Ardent Media. ISBN 0-9664902-6-6.
- ReproLine The Reading Room. Lactational Amenorrhea Method, which cites:
:Zinaman M, Hughes V, Queenan J, Labbok M, Albertson B (1992). "Acute prolactin and oxytocin responses and milk yield to infant suckling and artificial methods of expression in lactating women.". Pediatrics 89 (3): 437–40. PMID 1741218.
- Sheila K. and John F. Kippley (November-December 1972). "The relation between breastfeeding and amenorrhea". Journal of obstetric, gynecologic, and neonatal nursing 1 (4): 15–21. PMID 4485271.
- Sheila Kippley (November-December 1986 and January-February 1987). "Breastfeeding survey results similar to 1971 study". The CCL News 13 (3): 10. and 13(4): 5.
- Task Force on Sudden Infant Death Syndrome (October 2011). "SIDS and Other Sleep-Related Infant Deaths: Expansion of Recommendations for a Safe Infant Sleeping Environment". Pediatrics 128 (5): e1341–e1367. doi:10.1542/peds.2011-2285. PMID 22007003. 5.
-  Journal of Tropical Pediatrics Volume 28, Issue 1 Pp. 1