Parents to 3 teenagers and we just found out I’m pregnant

Like the title says, my husband (39M) and I (40F) have 3 teenagers and we just found out I’m pregnant. This is an unexpected, unplanned pregnancy so needless to say, we’re both in reeling. It’s very early days, so we won’t be telling the kids until I’ve been to the doctor and can confirm that things are progressing well.

I’m sure the kids will be excited after the shock wears off because they’ve been begging for a younger sibling for years, but I also know it will be a huge adjustment and will kind of upend our lives.

I’m most worried about my youngest who is almost 13. She has ADHD and while I notice a big difference for her when she takes medication, she doesn’t like it. I’m trying to respect her choice in, so she’s currently unmedicated and I don’t anticipate this changing anytime soon.

However, without medication, she struggles more with emotional regulation and gets overwhelmed easily. She sometimes cries over tiny things and doesn’t have much of an attention span. She’s been the youngest her whole life, so I’m worried that this news will hit her the hardest even if she’s excited at first.

What are things I can do to help her adjust to the idea and prepare for how things will change?
Anything I should definitely not do?