Breach of confidential information-Advice needed

Hi ladies I'm just after a bit of advice....it's a little complicated but bare with me.... I work in the rail industry, my job is very physical. I had a fall on some stairs last week and hurt my back, I put it in our accident book and was sent to a local walk in clinic to be assessed, I also felt it necessary to tell the shift manager about my pregnancy because I was worried. Because of the duty of care system and the shift change it meant 6 managers in my place of work were inform of my early pregnancy. After my return from the walk in clinic I went to see one of the managers on duty and explained that only my husband knew about it and we would like to keep it that way until we had got past 12 weeks. I was assured that all the managers will be spoken to and be told to keep it confidential. On Friday someone asked my husband, who works at the same place if I was pregnant saying that a few people were talking about it in the mess room and that someone had been told by a "reliable source". I am angry and devastated as it was my news to share and no one else had the right, especially a manager who is in a position of trust. It has also forced us to tell our family early as we were then worried someone would put something on Facebook or tell other family who also work for the same company. To be able to take this further, it means telling more people (union reps). What would you do and any advice?