In our case, I found out the marketing list from Enfamil and bought it for my zip code. I complained to the hospitals’ privacy officer and the state regulator and found that everything was legal.
There is a lot of data on the topic...
Prescriptions: https://www.theguardian.com/technology/2017/jan/10/medical-d... Linkage to lifestyle data: https://www.statnews.com/2018/07/18/health-insurers-personal...
In our case, the hospital pharmacy issued drugs to her indicative of a pregnancy. The pharmacy or insurer provides that information in real time to data brokers. The pharmaceutical companies assign quotas and send salespeople for certain drugs. There are other ways for data to get out that we’re not certain of. Perhaps the insurer “anonymizes” and sells subrogation information. Or the lab. In any case, they knew that my wife was admitted to an OB floor of a hospital, but didn’t know the outcome.
It’s not going away. The US government uses these same techniques with companies like Google to combat extremism or terrorist conversions — they actually use factors like this to target potential recruits with counter-information via ads.