Exposed to nitrous oxide

I just went to the dentist for my 4 year old son to have cavities filled. The dentist administered laughing gas via a nose mask. It was only maybe 10-15 minutes at most. I was also wearing a mask as it’s required because of pandemic. After doing research of general anesthesia for dental procedures for kids since the laughing has didn’t work for my son. He didn’t get his cavities filled. I came across that pregnant woman should not be exposed to laughing gas. No one told me anything or was on any of the paperwork I signed for my son. The dentist or dental assistant mentioned nothing. Mind you I’m five months pregnant, so I am showing. I’m assuming I had very little exposure. I called the dental office to confirm if it’s safe to be around when pregnant. They said after the 1st trimester it’s ok to be around. Although that is different from what came up on the internet. Does anyone know if it’s safe after 1st trimester? I’m upset at myself for not researching before hand and at the fact no one mentions anything while I was in the room with my son.