With genetic testing, it is now possible to determine many things about a baby before it born. It is routine to run a genetic test in order to ensure that a baby is healthy and normal. If the baby will not be "normal" the parents are given the choice not to continue the pregnancy (which could also be translated as "have an abortion".) Some people consider it wrong to bring into the world a child who will not be "normal". For many people with inherited disabilities, the idea of testing for disabilities is offensive. To them, it means they are not special human beings like everyone.
In the book and movie My Sister's Keeper, two parents have a "designer baby" genetically created to be a blood/organ donor for her sister with cancer (which could also be translated to "spare parts".) Nowadays, families with genetic diseases can arrange to have such a baby. The DNA of each fertilized egg is examined for the defect that passes on the disease. When one is found without the defect, it is placed in the womb.
However, not every such baby is created because of a genetic defect. Some, like the one in My Sister's Keeper, are designed with a certain blood type. Some are created to have certain characteristics, such as black hair or blue eyes. Perhaps the parents wanted a boy or girl. It is becoming easier and cheaper to have a "designer baby", and it causes young couples to make difficult decisions.