hmmm, I don't know.
I mean, I can (kind of) follow your thinking. but (and it's a big but):
ostensibly when pregnant with dd1, I was not stressed. well, apart from the standard freaking out what-have-I-done-ness of it, and the hyperemesis, etc. there was, however a really interesting study that someone linked to ages ago which was sort of along these lines - to do with (for want of a better phrase) emotional stress amongst immigrant mothers (no family support, not understanding new culture etc) and the likelihood of this being a factor in ASD. I found it interesting because I was that person, in a way - we were abroad when I was having dd, living in a very different culture, with no family at all (either of us) and I was totally unsupported. and then very ill, with all the stress that brings, hospitalised a couple of times - essentially marooned in hospital as dh was off on business trips a lot etc.
so, maybe it was all a contributing factor?
BUT, then, tbh, the stress I was under when pregnant with dd2 was much, much greater. I had a child with severe ASD, which all the professionals around me were doing their best to deny (dd1 was dx'd at just over 2.6 - weeks after dd2 was born, so all through that pregnancy I was being pushed from pillar to post, ignored, veiled threats re: PND (and implictions of Munchausen's) etc). that, along with the day to day stress of hyperemesis (again!), actually trying to relate to dd1 (at this point she literally would sit in the corner of a room and scratch the wall until her fingers bled. and screech and howl if I moved her away. no interest in anyone or anything else. at all. aside from food.), research what to do since no one else was helping etc. plus a load of incidental stuff - dh's job went tits up and we were broke, we were rebuilding the house - literally every room in the house was a building site apart from dd1's bedroom. and dh had 2 major life threatening operations, back to back.
I think on balance, dd2's pregnancy wins out on stress - and she is the less ASD one (I say less, she has no dx, and none likely. but she is not completely NT, just comparatively so when you factor in dd1)
anecdotal, sure. but you have to start somewhere.
do you think your stress was greater with your ds' preganacy than with your dd's? (sorry, personal question. but I wondered where your initial belief comes from, if not from personal experience.)