See related article by Greensides.
Corticosteroids are a synthetic version of the stress hormone cortisol. As such, they have manifold effects across systems and functions of the body including renal, vascular, endocrine, central nervous system, skin, gut, and—of most relevance for their use for imminent preterm labor—growth and development and immunological function (and, therefore, response to infection).
We have evidence for the protective efficacy of antenatal corticosteroids, dating back to animal studies in the 1960s and clinical trials beginning in the 1970s. Roberts and Dalziel's Cochrane reviews1 summarize the findings of these trials (mainly from high-income countries), notably that treatment with antenatal corticosteroids prior to imminent preterm birth, compared with placebo or no treatment, is associated with:
32% lower neonatal mortality (relative risk, 0.69; 95% confidence interval, 0.59 to 0.81; N=7188; 22 studies, from the 2017 review), and
reduced risk of respiratory distress syndrome, intraventricular hemorrhage, necrotising enterocolitis, and systemic newborn infection in the first 48 hours of life.
On the strength of such evidence, corticosteroids have been a mainstay of preventive treatment for preterm birth in high-income countries for decades. Use in low- and middle-income countries (LMICs) has been much less widespread, and evidence much sparser. However, anticipating that such use could have particular benefit in settings with high newborn mortality, there have been prominent efforts at the global level to promote use in LMICs—dating from 2012—reflected in the World Health Organization's (WHO's) Born Too Soon report,2 the focus on antenatal corticosteroids by the UN Commission on Life-Saving Commodities for Women and Children,3 …