Preterm birth can be traumatic for some mothers, involving feelings of grief over the hoped-for full-term pregnancy. In this longitudinal study, we interviewed 50 mothers of preterm infants, using the reaction to diagnosis interview when their child was 1 month and 18 months old. We examined change and stability in resolution status over time. Additionally, we explored possible predictors of resolution trajectories between 1 and 18 months. Findings indicated that resolution at 1 month was not yet common. The rate of resolution at 18 months was 62.6%, compared with 38.2% at 1 month. Prenatal precursors of preterm birth, lower medical neonatal risk, and lower maternal stress at 1 month significantly differentiated mothers who attained resolution as early as at 1 month from those who were unresolved at 1 and 18 months. Lower maternal stress at 1 month was the only predictor that significantly differentiated initially unresolved mothers who later attained resolution from those who remained unresolved at 18 months. Discussion focuses on maternal stress, which may mark a subgroup of mothers of preterm infants who are at risk of being unresolved through the first 18 months, and who may benefit from resolution-focused intervention.