how to limit a trigger frequency?

Sorry for my English because it was written in google translator.

I'm trying to do programming that might limit the spawn of the enemy, but I do not know how to do it.

 public GameObject Inimigo;
 public float spawnTime;
 public Transform[] spawnPoints;



 // Use this for initialization
 void Start () {
     InvokeRepeating ("Spawn", spawnTime, spawnTime);
 }

 void Update(){

 }

 // Update is called once per frame
 void Spawn () {

     if(Vida_Jogador.Vida <= 0f){

         return;
     
     }
     int spawnPointIndex = UnityEngine.Random.Range (0, spawnPoints.Length);

     Instantiate (Inimigo, spawnPoints [spawnPointIndex].position, spawnPoints [spawnPointIndex].rotation);
 }