The sperm fertilizes the egg; the first cell is formed. 

This single cell then proceeds to multiply into two, four, then sixteen...

Is there any external impetus during this process?

There isn’t is there...

In that case, is there an external impetus when these cells continue to multiply and form various organs?

Now this is the very point hidden in the meaning of the twelfth and thirteenth verses of the Surah al-Mu’minun that I hope to highlight and bring to your attention...