I don't actually think that this is the proper usage of the phrase "pregnant pause." Where did you see this sentence?
Usually we use this phrase when we are talking about people having a conversation, or someone giving a speech. When the conversation or speech reaches a moment of silence, but that silence is full of meaning, that's called a "pregnant pause."
For example....The speaker told us she was going to reveal the secret to living a happy life, and then followed this with a pregnant pause to build suspense.