All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
It is permissible to delay having children for a temporary period for a specific benefit as in the case that you mentioned in the question, which is delaying having children until finishing studies. The Sharee’ah permitted this for a necessity, and the evidence for this is that Jaabir narrated that a man from the Ansaar came to the Prophet and said: "I have a female slave, and she is our servant and she carries water for us, and I have sexual intercourse with her, but I do not want her to be pregnant.” Thereupon the Prophet said: ''You may practice ‘Azl (coitus interruptus) if you so like, and it is only what Allaah decreed for her that will come to her.” [Muslim]
Moreover, Jaabir said: “We used to practice ‘Azl during the lifetime of the Prophet . This (the news of this practice) reached him and he did not forbid us from doing so.” [Muslim]
For more benefit, please refer to Fatwa 89833.
Allaah Knows best.