Eugenics is the applied science or the biosocial movement which advocates the use of practices aimed at improving the genetic composition of a population (
Unified Medical Language System)
When we think of eugenics we think of those practices -- in the extreme it would be the ones the Nazis used, such as forced sterilizations. Aborting undesirables fits into that conception. Or even more benign forms of coercion, like if they had to pay a tax for having undesirable child either directly or indirectly (e.g. more taxes on parents because of increases healthcare costs for their child or because the state believes it will have to collect money to support an 'unproductive' public charge)
Each individual couple freely making the decision to abort does not amount to a movement because there are no practices in place.