In a 33‑week‑gestation infant delivered by caesarean section to a diabetic mother who presents with grunting, respiratory distress, and cyanosis, what is the most likely diagnosis?

Respiratory Distress Syndrome (RDS) is the Most Likely Diagnosis

In this 33-week preterm infant delivered by cesarean section to a diabetic mother presenting with grunting, respiratory distress, and cyanosis, RDS (Option B) is the most probable diagnosis. 1

Why RDS is the Primary Diagnosis

Convergence of High-Risk Factors

• Prematurity at 33 weeks represents the single strongest risk factor, as surfactant deficiency is nearly universal in infants born before 34 weeks' gestation who develop respiratory distress 2

• Maternal diabetes compounds RDS risk through delayed fetal lung maturation, as maternal hyperglycemia directly inhibits surfactant production in the developing fetal lung 1

• Cesarean section delivery eliminates the beneficial thoracic compression that occurs during vaginal delivery, increasing the likelihood of both RDS and delayed lung fluid clearance 3

Classic Clinical Presentation

The triad of grunting, respiratory distress, and cyanosis within hours of birth is pathognomonic for surfactant deficiency:

• Grunting represents physiologic auto-PEEP as the infant attempts to maintain functional residual capacity 1
• Cyanosis reflects ventilation-perfusion mismatch from atelectatic alveoli 2
• The onset timing (typically within 3-4 hours of birth) matches this clinical scenario 3

Why Other Diagnoses Are Less Likely

TTN (Transient Tachypnea of the Newborn) - Option A

TTN is possible but less likely because:

• TTN typically presents with tachypnea as the predominant feature, not grunting and cyanosis 4
• TTN rarely causes severe cyanosis requiring significant oxygen supplementation 1
• The combination of maternal diabetes and prematurity makes RDS far more probable than simple delayed fluid clearance 1

Truncus Arteriosus - Option C

Truncus arteriosus is highly unlikely as the primary diagnosis because:

• This cyanotic congenital heart defect typically presents with a loud systolic murmur and signs of congestive heart failure, not isolated respiratory distress at birth 1
• The clinical presentation would include bounding pulses and progressive heart failure over days, not immediate respiratory distress 5
• Structural heart disease does not explain the specific risk factors present (prematurity, maternal diabetes, cesarean delivery) 1

PPHN (Persistent Pulmonary Hypertension of the Newborn) - Option D

PPHN is possible as a secondary complication but unlikely as the primary diagnosis because:

• PPHN more commonly occurs as a complication of other conditions such as meconium aspiration, severe RDS, or sepsis, rather than presenting de novo 1
• PPHN typically manifests with severe, refractory hypoxemia and labile oxygen saturations that are disproportionate to radiographic findings 1
• In this clinical scenario, PPHN would develop secondarily if initial RDS management fails 1

Immediate Management Algorithm

Initial Respiratory Support

1. Start with supplemental oxygen or CPAP rather than immediate intubation, as establishing adequate ventilation is the priority 1

2. Prepare for surfactant administration if oxygen requirements exceed 30-40% FiO₂ on CPAP 1

3. Administer prophylactic or early rescue surfactant (within 2 hours of birth) to reduce mortality by 47% (RR 0.53, NNT 9) in preterm infants with surfactant deficiency 2, 1

Critical Metabolic Monitoring

• Monitor blood glucose closely and maintain levels between 90-180 mg/dL during the transition period to prevent hypoglycemia and subsequent neurological injury in infants of diabetic mothers 1

Monitoring for Complications

• Watch for secondary PPHN development if initial management fails, as this represents a serious complication requiring escalation of care 1, 6

• Monitor for air leaks (pneumothorax, pulmonary interstitial emphysema), as delayed surfactant administration increases these risks 1

Common Pitfalls to Avoid

• Do not delay surfactant administration waiting for radiographic confirmation, as clinical presentation in a high-risk infant warrants early treatment 2

• Do not attribute all respiratory distress to TTN simply because of cesarean delivery; the combination of prematurity and maternal diabetes makes RDS far more likely 1, 4

• Do not miss hypoglycemia in infants of diabetic mothers, as this can compound respiratory distress and cause long-term neurological injury 1