I smoked cigarettes for many years and tried to quit a number of times, before I found a strategy that stuck. Four years later, I still haven’t picked the habit back up. Instead of total abstinence, what works for me is abstaining while I’m in my normal routine. So if I travel, I’ll have the odd cigarette. I smoke less than a pack a year, and it happens rarely. I treat it in a similar fashion as I do alcohol or sugar, and am able to do something I love in a way that doesn’t feel too detrimental to my health. While I was pregnant, I chose not to smoke at all. I hadn’t heard of any risk, but it didn’t feel worth it. Since having the baby (eight weeks ago now) and heading on a short road trip, I’ve wondered what the risks are to my breastfed baby if I smoke the odd cigarette. Is it worth avoiding cigarettes for another year, two, three?
I know this isn’t your question, but I want to flag here that your approach to this is a really important example of a harm reduction strategy in health behaviors, one that I wish we did more of. The health benefits of moving from continual smoking to smoking less than a pack a year are enormous, and there are a lot of situations in which total abstinence is infeasible. Just a good general lesson.
To your specific question: first, there was benefit from abstaining during pregnancy. Smoking during pregnancy is causally associated with lower birth weight. At the scale you are doing it, it’s basically impossible that those effects would be noticeable, but we do know there is a link there (based on randomized trials of smoking cessation).
During breastfeeding, nicotine and other cigarette products can be passed through breast milk. It’s also not good for your infant to be exposed directly to smoke. However: the half-life of cigarette chemicals in breast milk is limited. Within a few hours after smoking, any residual nicotine would be limited. In this way, if you wanted to have a cigarette away from your child and wait some period before nursing, that would come close to avoiding any risk.
Reality check: your smoking behavior is very unusual. Almost any data we have comparing smokers with non-smokers is focused on people who smoke regularly. Dosage here is extremely important. The idea that an odd cigarette or two would impact your infant is implausible. There are things you can do (waiting) to even further lower the risk, but note that already it seems extremely small.