"Dreams are like mirrors that reflect your emotional state. Many women (and, yes, sometimes even men), dream of being pregnant. The obvious intitial thought is that it is a sign that you are pregnant, if you are a female. Of course the dream might simply be a way for your subconscious mind to reflect back to you your hopes or maybe fears of pregnancy. Pregnancy in dreams often represents a new event about to take place in your life, a new creation of yours or a rebirth of yourself. It is generally very positive and indicates growth in your life!" Because you're embarking on a new phase in your educational life, i.e. starting a research degree next year, which you have already begun to work on, this may be representative of the 're-birth' signified in your dream.
"If you are giving birth [in your dream] think about what happens when a woman gives birth: there is pain, followed by new life. In this case, this could indicate something in your life that will be painful to deal with but will ultimately give you great joy. Or it could mean that there is something you want to bring into the world which will be as life changing as giving birth. Whatever it is, the good news is that it is a natural event, something spontaneous and filled with life." This signifies recently finishing the huge, difficult and life changing accomplishment of earning your Bachelor's degree, and now moving on to the next phase in your education.You can read more at the site below, the source of the quoted portions above:
I also think, because you are so dedicated to your educational life right now, you don't want to risk becoming pregnant at this time, because it would prevent you from achieving your goals, but once your studies are completed, you might be ready and/or would like to be a mother some day, and this is not on your mind, but in your subconscious.
I wish you the best of luck in your studies!