The Exclusive Breastfeeding method of birth control is also called the Lactational Amenorrhea Method of birth control, or LAM. Lactational amenorrhea refers to the natural postpartum infertility that occurs when a woman is not menstruating due to breastfeeding. Many mothers receive conflicting information on the subject of breastfeeding and fertility.
Exclusive breastfeeding has in fact been shown to be an excellent form of birth control, but there are certain criteria that must be met for breastfeeding to be used effectively.
Exclusive breastfeeding (by itself) is 98-99.5% effective in preventing pregnancy as long as all of the following conditions are met:
Your baby is less than six months old
Your menstrual periods have not yet returned
Baby is breastfeeding on cue (both day & night), and gets nothing but breastmilk or only token amounts of other foods.
How can I maximize my natural period of infertility?
Timing for the return to fertility varies greatly from woman to woman and depends upon baby's nursing pattern and how sensitive mom's body is to the hormones involved in lactation.
Breastfeeding frequency and total amount of time spent breastfeeding per 24 hours are the strongest factors leading to the return of fertility: a mother is more likely to see the return of fertility if baby's nursing frequency and/or duration is reduced, particularly if the change is abrupt.
In some populations, research has shown that night nursing slows the return to fertility.
One study showed that mothers who were separated from their infants (but expressed milk to provide 100% breastmilk for baby) had a higher pregnancy risk (5.2%) during the first 6 months (Valdes 2000).
The introduction of solid food can also be a factor in the return of fertility. Once baby starts solids (if mom's cycles have not returned), the natural period of infertility may be prolonged by breastfeeding before offering solids, starting solids gradually, and not restricting nursing.
You can achieve higher effectiveness by practicing ecological breastfeeding:
keeping baby close
breastfeeding on cue (day and night)
using breastfeeding to comfort your baby
breastfeeding in a lying-down position for naps and at night
using no bottles or pacifiers
If you practice ecological breastfeeding:
Chance of pregnancy is practically zero during the first three months, less than 2% between 3 and 6 months, and about 6% after 6 months (assuming mom's menstrual periods have not yet returned).
The average time for the return of menstrual periods is 14.6 months.
Moms whose cycles return early tend to be infertile for the first few cycles. Moms whose cycles return later are more likely to ovulate before their first period.
There are links to the research to back all of this up on the Kellymom website.