How much alcohol passes to your baby when you breastfeed?

If you drink when you are breastfeeding, how much alcohol passes to the baby? A simple question, but I have not seen the answer published anywhere in the public domain. In every statement on the safety of breastfeeding and drinking, this basic fact is omitted. Once again we are given plenty of statements advising us on how to behave, but not the basic information that would help us to make an informed decision for ourselves!

I have done some research and come up with this answer: your baby should not get more than 1% of what you drink. So if, for example, you drink a 175ml glass of wine and continue to breastfeed as normal, your baby might consume, at most, the equivalent of 1.7ml of wine. If on the other hand you drink a whole bottle of wine (750ml), your baby could get the amount of alcohol in 7.5ml of wine (that's one and a half teaspoons). It is not my aim to condemn,condone or otherwise advise, but simply to inform you.

In the rest of this post, I will try to convince you that this answer is right, or at least in the right ball park. First I will use a very simple argument, which I will then follow with a more detailed analysis based on blood alcohol data which is widely published. This analysis will also show that this estimate is quite conservative, and in most cases, if you only drink 1 or two drinks, your baby will be getting significantly smaller doses of alcohol than the 1% maximum.

First, we need some background
Alcohol that you consume enters your blood stream and is distributed around your entire body, including your milk. In fact alcohol passes so quickly into mother's milk that the concentration in your milk is essentially the same as that in your blood. However, what goes in, can also come out. As you sober up, the amount of alcohol in your blood falls, and the amount in your milk falls simultaneously.

In order to calculate the amount of alcohol consumed by the baby we will need to have an idea of how much milk the baby will drink. Of course you never know how much breast milk your baby takes, but we can hazard that it might be similar to a bottle fed baby, so your baby is not likely to drink more than say 250ml (1/4l). It is believed that an average baby will consume 570-900ml of milk per day (see Kellymom), and this is pretty much constant as the baby gets older until significant quantities of solids are consumed. The quantity of milk remains pretty much constant while the consistency and quality of the milk adjusts over the months to meet your child's changing needs.

A simple (and not very accurate) argument
When you have a drink, be it large or small, the alcohol you consume enters your blood stream and circulates around you entire body. I weigh 55 kg, and this equates to approximately 55l of meat, bone, gristle and blood. If we assume that the alcohol is uniformly dispersed throughout the body, including mother's milk, then each litre of my body contains 1/55th (or 1.8%) of the alcohol I consumed. When my baby drinks 1/4l of milk, he will be getting 1/(55*4) =0.5% of the alcohol that I drank.

Further analysis
In the simple argument above, there are a number of assumptions which may not be accurate:

1. My body's density may not be 1 kg/l, so although it is true that I weight 55kg, this might not be exactly 55l.
   
2. Alcohol may not disperse to all body parts equally.
3. If you only have one drink, then probably 250ml is a safe upper limit on how much your baby might consume while you are under the influence. However, this might not be true if you drink several drinks.
   
4. Your milk alcohol content might not be at its highest when you feed your baby.
   

The first two limitations of my argument can be addressed by remembering that milk alcohol content (MAC) is the same as blood alcohol content (BAC), and using widely published data which relates number of drinks consumed to blood alcohol content. For instance, the table at:

http://www.statemaster.com/encyclopedia/Blood-alcohol-content/

Using this table we can see that after consuming a "standard drink" containing 18ml of alcohol, a woman weighing 55kg will have a peak blood alcohol content of 0.04%, or 0.4 ml alcohol /litre of milk. So, our 250ml feed would contain approximately 0.1ml of alcohol. This is 0.1/18= 0.6% of the alcohol that I consumed. So, very close to the original figure I suggested of 0.5%. (Note also, that the blood content increases linearly with the number of drinks consumed, which means that our argument applies equally well to one or many drinks).

Now, so far all these calculations have been based on my body mass, but if you are smaller, then the concentration of alcohol in your blood and therefore in your milk will be a little higher. For a 40kg (6 st 6 lb ) lady the 0.6% becomes 0.7%.

Addressing points 3 and 4 is more tricky since there are many possible drinking and feeding patterns that we could consider. I will discuss this further in a later post. For now you should note that the results stated here are assuming that you drink all your drinks in a short space of time, then feeding your baby when you blood alcohol content is at its highest, but also assumes that you will only feed a maximum of 250ml to your baby while you are under the influence and that you will be sober before any further feeds. I expect that the figures given above will be fairly relevant to more realistic drinking patterns, but as a precaution I have simply rounded the figure up to give the 1%, as quoted at the beginning of this post.

Other considerations

There are many things to consider when deciding whether you will drink alcohol while breastfeeding. These include underdeveloped liver in very young/small babies, dehydration of the mother, effect on the let down response, and the fact that babies tend not to drink as much when you have been drinking. These factors are outside the scope of this post, but most are covered at Kellymom: http://www.kellymom.com/health/lifestyle/alcohol.html