Object Instantiate two times when i SetParent

Hi, I'm trying to instantiate a number X of gameObjects as children of a gameObject A (on which the script is attached). when i'm instantiating them not as children, everythings goes as planned.

But when i SetParent them, another gameObject gets instantiated as the child of the child of my gameObject A.

Here's the code where the magic happens. The fact that i use a coroutine change nothing the situation.

     IEnumerator CreateSpineDeformation(float halfSizeY, float scaleCoefficient, int iterations)
     {
         GameObject deformation = Instantiate(gameObject) as GameObject;
         deformation.transform.position = transform.position + Vector3.up * halfSizeY;
 
         deformation.transform.localScale = transform.localScale / scaleCoefficient;
 
         deformation.transform.RotateAround(transform.position, transform.up, UnityEngine.Random.Range(rotateUpCoef * -1, rotateUpCoef));
         deformation.transform.RotateAround(transform.position, transform.right, UnityEngine.Random.Range(rotateRightCoef * -1, rotateRightCoef));
         deformation.transform.RotateAround(transform.position, transform.forward, UnityEngine.Random.Range(rotateForwardCoef * -1, rotateForwardCoef));
 
         deformation.transform.SetParent(transform); //HERE
 
         DeformationManager deformationManager = deformation.GetComponent<DeformationManager>();
         deformationManager.iterations = iterations;
         deformationManager.scaleCoefficient = scaleCoefficient;
         deformationManager.sources = 1;
         yield return null;
     }

Here is where i call it

 void StartDeformation() {
     for (int i = 0; i < sources && iterations > 0; i++) {
         StartCoroutine(CreateSpineDeformation(source.GetComponent<Renderer>().bounds.size.y / spawnPositionRatio, scaleCoefficient, iterations - 1));
     }
 }

It's my first time uploading to this forum. Hopes i'm posting right. Thank you !