It turns out that positive quad screen results can also be indicative of fetal demise. The fact that the test screened positive for three different anomalies means that probably none of them were the actual problem.
At 17w3d the u/s only measured 14w5d, just after my last appointment. So, D&E tomorrow and then my husband is taking me to Hawaii next week for some kind of tropical recuperation.
I will probably write about this more later, just to process everything for myself, but right at this moment I can barely manage to type. I am just going to go out for a real espresso now and get a fabulous bottle of wine for later, and try to figure out how to tell my daughter about this.