Designer Babies, or genetically modified babies, were first introduced as a concept in the 1970's. It wasn't until the 90's that the research was picked back up. In 2000, a girl was born with a rare genetic disorder called Fanconi anaemia, and she needed bone marrow from genetics that were almost the same as hers. The doctors used a scientific process called pre-implantation genetic diagnosis (PGD) to make what some referred to as the "test tube baby." This was never repeated because of the ethical concerns surrounding the process. The designer baby controvery would have picked up right before Ishiguro released Never Let Me Go, and there are traces of it's presence in the novel. The reader infers that because the characters were created as clones, they had to be scientifically manufactured in some way. Many readers will see this cloning process similar to the Designer Baby process. The author creates this image in the head of readers to warn them amount the controversies and ethics regarding genetically modifying people. 

BBC News | HEALTH | Baby created to save older sister

Designer Babies - Engineering the Perfect Baby