Objectives: To investigate factors contributing to separation and divorce in first-time parents. Methods: Quantitatively analyzing data using Mann–Whitney-U-test, Chi-square and logistic regression analysis test from separated and non-separated mothers and fathers, when first child was six months and four years of age. Outcome measures were quality of dyadic relationship, QDR-index and its dimensions and variables. Also, a qualitative content analysis of comments to one open question about contributing factors to the experienced situation from the separated parents (n = 39) was conducted. Results: The experienced quality of the relationship measured with QDR-index and especially Dyadic Satisfaction, Dyadic Consensus and also Dyadic Cohesion showed a statistically secured difference between the groups of separated and non-separated parents. The qualitative description showed seven categories of factors contributing to separation: Strains from parenthood, Stressful conditions, Lack of intimacy, Insufficient communication, Differing personalities & interests, No commitment, and Negative effects of addiction. The described factors were in accordance with the factors described in earlier non-Swedish research. Some of the factors may be possibly prevented from leading to separation, such as lack of equality, insufficient communication and lack of intimacy. Conclusion: Primary health professionals meet the majority of parents-to-be and new parents and should therefore take on the task of supporting them in their relationships, thereby helping to prevent unnecessary separations.