Final answer:
In a baby born at 26 weeks gestation who is not breathing after initial care, the correct step is to start Positive Pressure Ventilation (PPV) by mask due to immature lung development and the need for supplemental oxygen.
Step-by-step explanation:
If a baby born at 26 weeks gestation is not breathing at nearly 1-minute old after initial steps of care have been completed, the most appropriate next step is to begin Positive Pressure Ventilation (PPV) by mask. As per neonatal resuscitation protocols, if a newborn is not breathing despite stimulation, it is critical to support their breathing using PPV. Premature infants often require supplemental oxygen because their lungs are not fully developed, and they may lack sufficient pulmonary surfactant, which is essential for lung function. In a baby born as early as 26 weeks, the structures for gas exchange may not have formed adequately, and surfactant levels may not be sufficient for effective lung compliance. Thus, prompt respiratory support with PPV is essential for survival.