We did not do MaterniT21 test only because my pregnancy started out with triplets - one did not make it past 6.5 weeks. It's possible that triplet had a trisomy, so if I were to get a "positive for trisomy" result back -- it could be a "false" positive that has nothing to do with my surviving twins. But, I'd HAVE to get more invasive testing then, to be sure. Because of that possibility - we decided it wasn't a great option for us. Nothing is ever simple! ;-)