How do corticosteroids (steroids) mature a baby's lungs?

From the Guidelines

Corticosteroids accelerate the production of surfactant in a baby's lungs, reducing the risk of respiratory distress syndrome and improving lung maturity, with the most effective treatment being two 12mg doses of betamethasone 24 hours apart, as recommended by the most recent study 1.

Mechanism of Action

The corticosteroids stimulate type II pneumocytes in the fetal lungs to produce surfactant, which reduces surface tension in the air sacs (alveoli), making breathing easier after birth. This treatment significantly reduces the risk of respiratory distress syndrome, intraventricular hemorrhage, and neonatal death in premature infants.

Key Findings

• The use of antenatal corticosteroids has been shown to decrease mortality, the severity of respiratory distress syndrome, surfactant use, and intraventricular hemorrhage in infants of <34 weeks’ gestation 1.
• A systematic review and meta-analysis that included 6 RCTs evaluating the impact of antenatal corticosteroids on neonatal respiratory morbidity when given at 34 weeks of gestation further supported these findings 1.
• The administration of antenatal corticosteroids has been widely adopted as the standard of care in the treatment of people at risk of preterm delivery before 37 weeks of gestation, with the primary goal of reducing neonatal morbidity.

Recommendations

• Offer a single course of antenatal corticosteroids (2 doses of 12 mg of intramuscular betamethasone 24 hours apart) to patients who meet the inclusion criteria of the ALPS trial, ie, those with a singleton pregnancy between 34 0/7 and 36 6/7 weeks of gestation who are at high risk of preterm birth within the next 7 days and before 37 weeks of gestation 1.
• Consideration for the use of antenatal corticosteroids in select populations not included in the original ALPS trial, such as patients with multiple gestations reduced to a singleton gestation on or after 14 0/7 weeks of gestation, patients with fetal anomalies, or those who are expected to deliver in <12 hours.

Important Considerations

• The beneficial effects of antenatal corticosteroids last about 7 days, and the treatment is most effective when given 24-48 hours before delivery.
• The steroids also promote structural maturation of the lungs, including thinning of the air-blood barrier and increased lung compliance.
• This treatment may be considered at other gestational ages when preterm birth is imminent.

From the Research

Mechanism of Corticosteroids in Maturing Baby's Lungs

• Corticosteroids stimulate the production of surfactant phospholipids by alveolar type II cells, enhance the expression of surfactant-associated proteins, reduce microvascular permeability, and accelerate overall structural maturation of the lungs 2.
• Antenatal corticosteroid therapy improves both fetal lung mechanics and gas exchange due to accelerated morphologic development of type one and two pneumocytes, and enhances the production of surfactant binding proteins and fetal lung antioxidant enzymes 3.

Effects of Corticosteroids on Fetal Lung Maturation

• Treatment with antenatal corticosteroids reduces the risk of perinatal death, neonatal death, and respiratory distress syndrome (RDS) 4, 5.
• Antenatal corticosteroids probably reduce the risk of intraventricular haemorrhage (IVH) and have little to no effect on birthweight 5.
• A single course of antenatal corticosteroids is effective in accelerating fetal lung maturation in women at risk of preterm birth 4, 5.

Administration and Dosage of Corticosteroids

• A single course of antenatal corticosteroids is advocated between 24 and 34 weeks' gestation with either betamethasone or dexamethasone 3.
• The optimal time interval between corticosteroid administration and delivery is reported to be 1-7 days 3.
• Weekly repeat courses may reduce the occurrences and severity of respiratory diseases, but are associated with reduced fetal growth 3.

Benefits and Risks of Corticosteroids

• Antenatal corticosteroids do not increase the risk of death, chorioamnionitis, or puerperal sepsis in the mother 4.
• Treatment with antenatal corticosteroids is associated with a reduction in neonatal morbidity and mortality, including RDS, cerebroventricular haemorrhage, and necrotising enterocolitis 4, 5.
• Antenatal corticosteroids may be harmful in growth-restricted fetuses associated with an absent or reversed end-diastolic UA flow, as they are at increased risk of acidosis and perinatal death 3.