Less than 2% of the alcohol consumed by the mother reaches her blood and milk. Alcohol peaks in mom's blood and milk approximately 1/2-1 hour after drinking (but there is considerable variation from person to person, depending upon how much food was eaten in the same time period, mom's body weight and percentage of body fat, etc.). Alcohol does not accumulate in breastmilk, but leaves the milk as it leaves the blood; so when your blood alcohol levels are back down, so are your milk alcohol levels.
Always keep in mind the baby's age when considering the effect of alcohol. A newborn has a very immature liver, so minute amounts of alcohol would be more of a burden. Up until around 3 months of age, infants detoxify alcohol at around half the rate of an adult. An older baby or toddler can metabolize the alcohol more quickly.
Effects of alcohol on breastfeeding and the breastfed baby
* Alcohol does not increase milk production. In fact, babies nurse more frequently but take in less milk in the 3-4 hours after mom has had a drink, and one study showed a 23% decrease in milk volume with one drink (Mennella & Beauchamp 1991, 1993; Mennella 1997, 1999).
* 2+ drinks may inhibit let-down (Coiro et al 1992; Cobo 1974).
* One study showed changes in the infant's sleep-wake patterning after short-term exposure to small amounts of alcohol in breastmilk -- infants whose mothers were light drinkers slept less (Mennella & Gerrish 1998).
* Daily consumption of alcohol has been shown in the research to increase the risk for slow weight gain in the infant.
* Daily consumption of alcohol (1+ drinks daily) has been associated with a decrease in gross motor development (Little et al 1989).