Parents choosing for fertility treatment such as IVF do not *ask* for multiples. There is an increased chance of getting twins or higher multiples after fertility treatment, but the main concern of the parents usually is to get one healthy baby.
When using IVF-treatment, putting back two fertilized eggs instead of one, increases the chance of getting pregnant at all, commonly resulting in one healthy baby. But sometimes one of the fertilized egg splits during the first week, resulting in identical twins. In very rare occasions both fertilized eggs split, resulting in 2 identical twins during one pregnancy!