NEW YORK (Reuters Health) – New research from Japan suggests that antenatal corticosteroids promote survival in extremely preterm infants born at 22 to 23 weeks gestation.

Based on their observations from a look back at more than 11,000 infants, the clinicians say antenatal corticosteroids “should be considered” for threatened preterm birth at 22 to 23 weeks gestation.

The study, published online February 21 in The Journal of Pediatrics, “was one of the rare opportunities to look into whether antenatal steroids are effective in pregnant women before 24 weeks,” Dr. Rintaro Mori of the University of Tokyo noted in an e-mail to Reuters Health.

The study team analyzed outcomes for 11,607 infants born at 22 to 33 weeks gestation between 2003 and 2007 at 87 tertiary hospitals participating in the Neonatal Research Network of Japan. Antenatal corticosteroids were administered to 42% of the mothers who delivered between 22 and 33 weeks gestation.

The researchers found that antenatal corticosteroid use was associated with a reduction in acute respiratory distress syndrome, surfactant use, duration of oxygen therapy, as well as intraventricular hemorrhage in preterm infants born at 24 to 29 weeks gestation, but not in those born at less than 24 weeks gestation.

Antenatal steroid use had no effect on chronic lung disease, patent ductus arteriosus, or necrotizing enterocolitis in any gestational age group or overall, the researchers report.

However, the researchers say the Cox regression survival analysis produced the “most important” finding of the study – a nearly 30% reduction in mortality with antenatal corticosteroid use in preterm infants born at 22 or 23 weeks gestation (adjusted hazard ratio, 0.72; P = 0.03). This effect was also seen at 24 to 25 and 26 to 27 weeks of gestation and in the overall study population (adjusted hazard ratio, 0.69; P < 0.001). “The study,” Dr. Mori commented, “showed that antenatal steroid was actually effective not to maturate (the) fetal lung but to promote their survival.” “It was believed,” Dr. Mori explained, “that steroid given to pregnant women with threatened preterm labour after 24 weeks of gestation promoted fetal lung maturation and therefore survival. Fetal lung before 24 weeks’ gestation, however, is in a different stage of development and it was believed that there would not be any effect for pregnant women before 24 weeks.” The current observations suggest that there are effects of antenatal steroids on systems other than fetal lung maturation that may help reduce mortality of extremely preterm infants. “In the past, antenatal steroid was recommended for pregnant women between 24 and 34 weeks,” “Based upon this study, all obstetricians should consider giving steroid for women with preterm labour before 24 weeks, as well,” Dr. Mori told Reuters Health. The Journal of Pediatrics, Published Online February 21, 2011.