SIL’s Pregnancy Announcement at Birthday Party Causes Drama

Last week, my family had a joint birthday celebration for me (33F) and my brother-in-law (25M). This is typical for all family birthdays. It was hosted at my house, where my in-laws have been living with my husband and me for the past 2.5 years while they look for a home.

5 minutes after everyone arrived, my MIL said, “Okay, let’s eat,” so I went into the kitchen to make my plate. At the same time, my sister stepped into the laundry room to sign a birthday card.

While I was still in the kitchen, I heard my SIL say, “Mom and Dad need to open this together.” I didn’t know what she was referring to, so I stayed in the kitchen. Then I heard my MIL say, “Oh my God, is this real?” My sister came back and asked what was going on, and I said I thought my SIL had just announced she’s pregnant.

Because we weren’t in the room when it happened my sister and I stayed in the kitchen for a moment. My MIL then came into the kitchen and showed me the box. I said something along the lines of, “Yeah, I heard.” I then went into the living room and asked my BIL a few polite questions about their plans, (SIL was in the kitchen getting lunch) and the celebration continued.

About an hour and a half later, my SIL suddenly started crying and said she wanted to leave. I overheard my MIL say, “That’s just how some people are.” After they left, my MIL came back in and I asked what had happened. She told me my SIL was upset because she felt no one seemed excited about the pregnancy.

I explained that I wasn’t in the room when it was announced, that the announcement was framed as a gift for my MIL and FIL, and that this was supposed to be a birthday celebration. I mentioned that announcing a pregnancy at someone else’s birthday was common etiquette to not do. MIL said it was also BIL birthday celebration so it was fine.

MIL said there wasn’t anything selfish about it and I should have been more excited. BIL (21M) agreed with her and asked what else they were supposed to do.

I said they could have chosen any other day to announce. Christmas Eve was three days away. My MIL responded that my SIL couldn’t wait because there was deli meat being served at the party (SIL ended up eating some anyway after heating it up).

Since then, we haven’t spoken, and my in-laws decided to spend Christmas at my SIL’s house instead.

Everyone I have told about the situation has agreed with me however I need some outside opinions due to these reactions from them. AITA?

Edited to add: it’s hardly about being overshadowed at a family birthday party although that is a valid reason. The reaction came from SIL making rude comments to MIL saying “you’re unemployed so you’re going to do my nursery right”. This is a typical comment from her. Other common comments are usually about MIL weight and appearance. Makes it hard to be happy for someone who consistently acts like this. And everyone condones this behavior and doesn’t chastise her for it.