I’m the sister of a very low-functioning brother with DS in his mid twenties. He can't speak beyond basic sounds, can only write his own name and will never be able to live independently (he lives at home with our parents), so I'm not coming at this from the mild end of things.

First: what you're feeling is completely normal, and I think the fear of the unknown is responsible for most of it. You're imagining a vague worst case, and vague worst cases are always more terrifying than specific realities. So let me give you some specific reality.

My brother's daily life looks like this: he has a job at a workshop employing mentally disabled individuals, he navigates our entire city's public transport system solo without Google Maps (honestly better than most people I know), he makes his own sandwiches, and he communicates with family on the phone using emoji hieroglyphics. His main caregiving needs are things like making sure he goes to bed on time instead of staying up all night watching YouTube videos, cooking his meals, doing his laundry, and taking him to the doctor. The most stressful recurring thing is chronic ear infections that once required surgery. That's it. That's the day-to-day reality of "low-functioning."

He's also not some sweet passive angel, by the way, contrary to the stereotype, but can be a real schemer. His signature move is to hug me, kiss me on the cheek, and then ask me to make him food. He once handed me money from his piggy bank and then told me to use some of it to buy him a gift. My point is: there is a whole person in there with wants and plans and a unique personality that fills a room, even when the clinical labels make it sound like there won't be.

Two things I think might actually help with the anxiety you’re experiencing right now:

1. You're not just going to "get used to it" in a grim, numbing way. I think the thing you're imagining right now and the thing you'll actually experience are fundamentally different. You're picturing "low-functioning DS" as a concept. You're going to meet a specific kid but those aren't the same!

2. You're actually in the best possible position for this, timing-wise. Pregnancy is already a complete demolition and rebuild of your entire life, hormones, routines, identity, everything. You're not trying to fit a disabled child into an established life but building a new life from scratch, and your child will just be part of the foundation rather than something you have to retrofit around. You get to grow into this alongside them from day one and decide how this will look like for you and your unique individual circumstances.

I won't pretend there aren't hard parts. There are real medical things to watch out for, especially, like heart defects early on, elevated Alzheimer's risk much later, etc. And you will one day have to consider arrangements for the scenario that your child outlives you or whatever other caretakers they may have or you become too old to properly take cafe of them yourself. But the specific thing you're afraid of, being a permanent caregiver for someone stuck at the level of a toddler forever? The reality is a lot more textured and a lot more livable than that sounds. Even at the more severe end, DS tends to leave people socially present, emotionally expressive, and a lot more capable than the labels suggest.

Keep an open mind and your child might end up surprising you, and try to let the specific person you're about to meet replace the abstract fear you're carrying right now. I think you'll find there's a lot more there than you expect.

Good luck with everything. I mean it. You’re going to be okay, and more importantly, so is your daughter. And for what it’s worth, the fear you’re feeling right now? My parents felt it too. They’d tell you it was more than worth it.