Yeah any time after about 16 weeks is too late for surgery.
Like I say I'm not sure if it's different in France. In the uk, if you are after 20 weeks you need to go to a specialist fetal medicine unit to have an injection to stop the baby's heart before delivery. It is kinder as sometimes they can survive birth at this gestation (this is how it was explained to me) I'm not sure if they do this in France.
Whatever gestation you are at the next bit it the same. They will give you a tablet to take which suppresses the pregnancy hormones and tarts getting your body ready for labour. It takes 48 hours to work, very occasionally it will work in less time but it generally doesn't in cases of terminations (I had the same with ds who had died over a week before and it still didn't kick off early)
After 48 hours you will go back into hospital to be induced. They will start it off with a pessary in the vagina (and an antibiotic one in your bum which surprised me!) then you will be given tablets orally every 3 hours. I had the pessary at 9am, I had 2 sets of tablets and dd2 was born at 4 pm.
You will be written up for any pain relief you want. I had codine, gas and air, oral morphine and in the end intravenous morphine on a button (can't remember what it's called). I used morphine and gas and air. The contractions can be pretty intense (it was the same with ds at 14 weeks but I didn't need morphine this time round) so don't feel you have to be brave about it.
In the uk you have an option to see and spend time with your baby. We were lucky, we named dd2, spent the night with her in a sands unit at the hospital. They dressed her and we took photos. The midwife took hand and foot prints and we have a memory box for her.
I'm not sure how much you know about T18. There are some physical features but they are not scary to see. Dd2 looked like a tiny normal sleeping baby. She had undeveloped ears, a smaller chin, locked arms at the shoulder and elbow and fingers that were crossed. I say this because the crossed fingers and possible 'rocker bottom' feet can effect the hand and foot prints, they can be a bit harder to get but our midwife was awesome and experienced at it. I've only fully noticed the effect when comparing them to ds prints that are much smaller but clearer.
If you have any other specific questions I'm more than happy to answer them. I've been entirely honest and factual, some of it is probably hard reading but I am the type of person who would rather know everything that will happen than be surprised on the day if that makes sense.