I have also had fetal tissue tested on
at least 3 occasions. Sadly, most
of the time
the answer
is not an obvious one. But I can practically guarantee that nothing you did (or didn't do) caused this.
Even if they tested the tissue and found no abnormalities, that doesn't really mean anything. They typically only test for 3..trisonomy 13, 18 and 21. But there are so many and so many different things that could have gone wrong. None of them your fault.