It wouldn't, and doesn't happen that term babies are aborted, just because. Ever.
Babies who have DS, when their mothers choose TFMR are, overwhelmingly, born shortly after the dating scan. Anomalies that necessitate a late TFMR often can't, or aren't picked up until the anatomy scan, which can be anywhere from 18-21w.
When a mother chooses compassionate induction for a late term baby, it's because that baby will suffer and then die. And the mother cannot bear to watch her darling baby fade away in pain.
Once you have been through the anatomy scan. Then there's a very detailed and lengthy follow up scan in fetal medicine, and then often another "making absolutely sure scan". You are referred to a specialist medical team who discuss your baby's diagnosis with you. There is often a bereavement MW present. You are given the full picture. Sometimes tests need to be done another few weeks down the line, so you wait, and hope, and pray. And google, and find articles and websites. Any knowledge or facts that you can.
If the worst happens, and your baby continues to deteriorate, or their prognosis/diagnosis becomes even poorer, then you have to choose. It's not a real choice. You spend the time between appointments desperately hoping that their heart will stop on its own so you don't have to choose. It's already your fault that they're poorly, now you have to make this choice for them. The hell of it is something I can't accurately describe.
You have to give birth regardless. And you pack a bag for a child that will never come home, and go to hospital knowing that you will leave with empty arms. You take a fluffy blanket to wrap them in, a book to read them "guess how much I love you". Maybe the baby bubble bath you'd already bought and put in the cupboard with a packet of newborn stashed nappies that you picked up after your 12w scan. "Getting prepared" you thought to yourself at the time.
I was encouraged to have a D&E under general anesthesia with my second TFMR but was made aware that they were generally only done up to 15/16w so I needed to think quickly as it becomes riskier for the mother. I didn't choose that method with either of mine.
You are told that they cannot feel pain yet, not before 26w, they're not sentient, their brains haven't developed those receptors. And you take that and hold it and hope that they only ever know warmth, love, and your heartbeat. That they've never known pain, fear, hunger and never will
Between then and 22w you give birth without having to consider the injection.
Post 22w then it is offered to have the injection. Not necessarily for all conditions, some babies will not survive the trauma of birth regardless of their gestation.
You have to sign things to say you understand that your baby won't be given medical assistance etc and you swallow a pill to begin your labour.
You give birth to your precious baby, name them and begin memory making, hand and footprints, reading them stories, sing to them, just being with them. You apologize "Mammy is so sorry, she's so sorry my baby, she loves you more than you can ever know". And you carry your cold, dead baby up to a mortuary, you kiss their head, weep and hand them to a nurse who will place them in a cold cot . You leave, amongst happy, excited new dads with car seats, waddling new mums who are smiling, content. Then you begin to plan their funeral and start a life which is different from the one before. You are forever changed. You are not the same person. And you can never be sure, if you share your story, that the person won't react with disgust at you and never look at you again in the same way. You can never be guaranteed kindness in your loss and grief.
Nobody would choose this because the baby was the sex they didn't want or because they didn't fancy being pregnant any longer. Nobody.
It is unpalatable for people to imagine a fully formed baby being "killed", but you cannot imagine the horror of having to live it. These are not unwanted babies, they have been planned for, hoped for, prayed for. They are named and remembered and loved.