This exact question is very close to home for me. My brother is severely intellectually handicapped, has dextrocardia (his heart is back to front and on the wrong sides) and has a list of congenital 'defects' as long as your arm. He also has a special type of epilepsy - and his fits are generally stress triggered.
My parents have been spoon feeding and changing nappies for 26 years now. They rarely (almost never) have a break, or time out or a night off - I was their chief babysitter and due to DH being in the Forces, we are regularly posted interstate away from my family, so it's just not an option anymore
Both my parents drink and smoke exhorbitant amounts - they are always telling me this is their only outlet considering they have no social life - and who am I to argue? I grew up ridiculously fast as a child - and spent every day after school looking after my brother and every day on the school holidays babysitting because my parents simply couldn't afford a carer with the high skills and training required to look after him. The impact and effect my brother has had on my family is immense. Don't get me wrong, we all love him dearly - and should anything happen to my parents, he will come and live with us - but that's a whole other story.
Every time my brother goes into hospital for any kind of treatment or surgery (which is quite often - any time he needs even something simple like dental work, it's a general anaesthetic), my parents have to sign the dreaded DNR form (Do Not Resuscitate) and come to an agreement that should something happen to him whilst under anaesthetic (very likely due to his heart issues) - do they Drs try and resuscitate him or not? My Dad says yes, he's his only son, my Mum says no - she is exhausted and if it's his time to go, then it's his time to go. This argument has torn my family apart on more occasions than I can count. We have all cried more tears over this one topic than anyone should in a lifetime.
My parents are regularly covered in bruises and marks where my brother has lashed out. He has the intellectual abilities of a 2yo, but trapped inside the body of a 26 yo and he is so incredibly strong. Puberty was hell for all of us - I still have scars.
When I fell PG with DS1, DH and I discussed what we would do if we found out our child had disabilities such as my brother's - and we both agreed, without question, we would terminate. When I fell pregnant with our current bump (21wks) - same thing.
I'm not saying it's a decision we made lightly - termination is final. You can't take it back. I love my brother but I would not wish my family's situation on my worst enemy sometimes, let alone the people I love most in the world.
Sorry this took so long to get out - but I felt I couldn't just say 'no, I wouldn't continue with the pregnancy' without some form of justification (even to myself) as to why.