I had my Down Syndrome son at age 39. I didn't have amnio due to the way he was positioned, but even so, I knew if he had Down S., I'd still have him. Perhaps if the birth defect were more severe, and I had amnio, I might have considered not having him.
Special considerations: I saw my doctor more often, at his insistence. I had gestational diabetes and also saw an internist/endocrinologist. (But ges. diabetes is more likely if a previous baby was very large, say eight pounds or over.)
I understood the risk of having a Down Syndrome child at my age. However, in my early childhood group, which the state of MA encourages women to join shortly after the child is born, there was an 18 year old and a 28 year old mother, both who had Down Syndrome children. Age matters, but Down Syndrome can happen at any age.
With my son, at age 39, I worked up until two weeks before his birth. I am not a super active person, but I was a teacher who 'taught on her feet' as I taught science which was a very active subject. (Well, the way I taught it.) But pregnant with my son, I needed more sleep and more 'sit-down time.' I did corridor duty sitting on a lab stool, though my principal told me to go sit at my desk and 'skip' corridor duty. Skip it? It was one of the few times I got to talk to the teachers in my corridor.
So, compared to the pregnancies I had at a younger age: more tired, sitting down more. (Once I got home I sat on the couch and held that position 'til bedtime. I had two daughters, ages 7 and 11 who ran around the house doing errands for me.) No morning sickness though, and a very uncomplicated, vaginal delivery.
My most difficult pregnancy was my first at age 26. Baby came early, was a frank breech and a C-section. My second two babies were HUGE and I managed a vaginal birth on each. And I am not huge myself, five foot, two inches and about 120 pounds.
Probably tmi here.