I know some of the reasons why my pregnancies were tough - hypermobility, for example, lack of good, nutritious food, stress poor choice of father, but other problems, no idea at all, they just were.
I certainly had an easier pregnancy with the second in terms of sickness, probably because my nutrition was better to begin with, so I could physically handle not being able to eat for a while, but I didn't actually have the brief period from 28-34 weeks where I felt really good that I did with the first, I had more backpain (much bigger baby in a different position and no money for an osteopath experienced in treating pregnancy related pain safely), surgical adhesions snapping for weeks as I grew bigger, I caught horrendous chickenpox that put me on oxygen and was really unwell afterwards for weeks until I began developing pre eclampsia in the last couple of weeks (also in a heatwave, which really didn't help).
But I was far, far healthier after birth with the second - I only started a massive flare of arthritis after about 9 months, instead of almost the second the first was born (but was dismissed by HCPs as being depressed).
Some of those things could be mitigated - which is why pregnant women get free prescriptions, dental treatment, etc - but there was no way to do that for other things, such as the pre existing conditions poor choice in men and twatty sexist medical staff.
It's just too complex an issue, as it's not just medical in terms of x happens in pregnancy when.. or y happens when somebody with z is pregnant, so it can be fixed by... , it's also social and financial, as well as being dependent where it can be helped through medical intervention on whether it's actually funded or made available to pregnant women (like physio that isn't for specific pregnancy conditions - not on offer, or medications that they can't or won't prescribe because 'pregnancy is a natural thing, I don't believe in prescribing anything in pregnancy [even when it's something known from years of research to be safe]'
Too many aspects. A reasonable inability to get trials on pregnant women past ethics committees. Sexism. Politics. Misogyny. Bad luck.