Background: Repetitive negative thinking (RNT; e.g., worry about the future, rumination about the past) and the tendency to interpret ambiguous information in negative ways (interpretation bias) are cognitive processes that play a maintaining role in anxiety and depression, and recent evidence has demonstrated that interpretation bias maintains RNT. In the context of perinatal mental health, RNT has received minimal research attention (despite the fact that it predicts later anxiety and depression), and interpretation bias remains unstudied (despite evidence that it maintains depression and anxiety which are common in this period). Method: We investigated the relationship between RNT, interpretation bias and psychopathology (depression, anxiety) in a pregnant sample (n = 133). We also recruited an age-matched sample of non-pregnant women (n = 104), to examine whether interpretation bias associated with RNT emerges for ambiguous stimuli regardless of its current personal relevance (i.e., pregnancy or non-pregnancy-related). Results: As predicted, for pregnant women, negative interpretation bias, RNT, depression and anxiety were all positively associated. Interpretation bias was evident to the same degree for material that was salient (pregnancy-related) and non-salient (general), and pregnant and non-pregnant women did not differ. RNT was associated with interpretation bias for all stimuli and across the full sample. Conclusion: Our findings highlight the need to further investigate the impact of interpretation bias in pregnant women, and test the effectiveness of interventions which promote positive interpretations in reducing RNT in the perinatal period.