The use of the word pregnant here refers to the phrase pregnant with meaning. The narrator is trying to salvage the relationship he has with his lover, he's trying to communicate to her but there are long, stabbing silences when they try to talk about their problems, and he is dwelling on these moments, these 'pregnant pauses', searching for possible clues in them over how their relationship is going.
The use of the word pregnant here refers to the phrase pregnant with meaning. The narrator is trying to salvage the relationship he has with his lover, he's trying to communicate to her but there are long, stabbing silences when they try to talk about their problems, and he is dwelling on these moments, these 'pregnant pauses', searching for possible clues in them over how their relationship is going.