Objective: Factors associated with maternal functioning in biological mothers whose infants were admitted to a Neonatal Intensive Care Unit (NICU) were identified as measured by a modified version of the Barkin Index of Maternal Functioning. Materials and Methods: This multivariable regression analysis explored sociodemographic and clinical data from 146 mother-infant dyads admitted to a Level III NICU between February 2015 and May 2016. Eligible dyads included: (1) adult biological mothers with singleton infants discharged home alive after NICU admission meeting criteria and (2) infants discharged home alive from the NICU with adult, biological mothers after a minimum 6-day admission. Results: Lower scores on the Edinburgh Postnatal Depression Scale (p < 0.0001), and an infant admission diagnosis of hypoglycemia (p = 0.0295) were significantly associated with higher levels of maternal functioning. Conclusions: The significant association between maternal functioning and depressive symptom score is corroborated by the literature. Results relative to a diagnosis of infant hypoglycemia and higher levels of maternal functioning are intriguing, considering current literature linking increased postpartum depression to gestational diabetes. The severity of other possible admission diagnoses may provide a partial explanation. We believe this is the first study suggesting a potential role between infant admission diagnosis and the level of maternal functioning.