In the United States, up to one-third of infants with a congenital anomaly require neonatal intensive care unit (NICU) hospitalization. Parents of these infants may have different decision-making priorities, which may be influenced by the timing of the infant's diagnosis. (1) To compare the ranked importance of decision-making beliefs for parents of infants who received a prenatal versus postnatal congenital diagnosis and (2) explore how parents describe their decision-making beliefs. A cross-sectional, sequential mixed-methods pilot design was applied to collect quantitative data using the Good Parent Ranking Exercise and further explore parents' decision-making beliefs through qualitative interviews. Maximum difference scaling/hierarchical Bayes estimation and content analysis were used to analyze the quantitative and qualitative data, respectively. Forty mothers completed the Good Parent Ranking Exercise and 20 mothers completed qualitative interviews. Four of the top 5 ranked parenting beliefs were shared by mothers in the prenatal and postnatal groups. Mothers in the postnatal group ranked "focusing on my child's quality of life" higher. Qualitative interviews revealed that previously identified decision-making beliefs were consistent in this NICU parent population, with 1 additional belief identified. Mixed-methods analysis revealed high concordance between the prenatal and postnatal groups. NICU nurses need to know that decision-making beliefs for parents who receive a prenatal versus postnatal congenital diagnosis, while largely similar, may have differences. Future research should explore decision-making beliefs in demographically diverse parent groups (ie, fathers, partnered vs nonpartnered couples) and effective strategies for promoting NICU parents' decision-making beliefs.