Because we all have very different genetic make-ups and immune systems.
I’m slim, size 10, was early 30s when I had DS. I was bad in pregnancy - PEP rash (horrific, basic a skin reaction as an allergy to your own baby), vomiting until 20 weeks, very tired and brain fog has never lifted.
DS is a toddler now, and I’m wiped out. He’s a busy little boy, but no more than most other NT toddlers. I’ve been subsequently wrecked by the birth and episiotomy scar that still hurts, and PND. My blood pressure sky rocketed after the birth.
I used to love the idea of a large family, but even if DH and I can face doing it again, I think my body would struggle to do this more than once more.
I have an autoimmune disease, and get laid very low for weeks by anything I catch (which is a lot now DS is at nursery).
I’d love to see what research, if any, DoHSC or academia is conducting in to this. I suspect it’s nowhere near enough, because women’s health and pregnancy is so overlooked and underfunded.