Question for seasoned dog owners

We have a beautiful sweet mastiff/rotti/lab mix who will be 2 years old this August. She’s definitely an energetic girl and always wants to say hi to every person and dog she sees. She’s been trained privately since she was little because we knew she would be a big dog, so we felt obedience classes would be smart. It was a great decision!

We live in a condo, luckily my schedule allows for 3 long walks/adventures a day which definitely tucker her out and we live right by a large park and escarpment that she gets to explore and play in during those walks.

We live on the 18th floor so her walks end with her and I taking the elevator back up to the condo, where she’s been trained to sit next to me and wait until the doors open and I give her an “okay” to walk when I walk.

She always enjoys when someone gets on the elevator and wants to say hi. Since she’s trained to sit beside me, when people ask if they can pet her we have them let her have a sniff and then she usually lifts her paw to “shake” and get some pets. Again, she loves the attention.

The past week or so though, she has given a “warning growl” to a few people when they’ve pet her. Even after she’s given her paw and looked at me for the okay to say hi. It’s so strange, she’s never growled at people before. She’ll let out playful growl sounds and inflections when my husband plays around with her, but this is different. It’s definitely a “back off” growl. My husband thinks it maybe because I’m pregnant. I’m at 22 weeks, and she has also been a little defensive when my husband tickles or plays around with me near my baby bump.

Could this growling (which again, she’s never done before) be a protective thing because of the baby? Or do any other fur mommies have any insight into why she may be doing this all of the sudden? She’s my first dog (husband grew up with dogs but she’s out first family dog) so I’m just not sure if there maybe other reasons why she would be doing this that I may not be picking up on🤷🏻‍♀️ thanks ladies!