Such dreams are mostly prophetic or simple brain chatter depending upon your current situation, what you see and experience in the dream. If the dreams are recurring, then it being prophetic is high probability.
Pregnancy symbolizes new beginnings. But, if you are a woman and already pregnant, then the dream is just your brain chatter and your anxieties of becoming a parent are reflected in the dream.
In almost all other situations, the dream indicates a major development that is likely to happen in the near future. If you dream of pregnancy of someone or yourself (women in particular) it may mean you need to be prepared for new beginnings in your life in the coming future. It may be a project, a new job, new school, business or something totally unexpected.
Your subconscious is nudging you to be prepared and wait to let whatever it is to take form. Being prepared and patience is the key here. If you had chosen a path of safety and let go of your passions (in terms of career), then the pregnancy dream symbolizes that you should now take the risk and follow your passion by taking the opportunity that arises. Your subconscious is pushing you to allow natural energies to work and let the destiny unfold.
Consider the dream as a guide and try to analyze your awake life. What is it that your heart desires? What is your passion? How prepared are you to take risk? Is your relationship with someone going to transform? In the similar lines the dream gives you a window to look at your opportunities and give you the confidence to pursue them.
Patience is the trick here. You cannot let yourself be anxious about these situations as you cannot have control on how long it will take to manifest itself.