Prenatal steroid therapy reduces the chance of respiratory complications among infants born at 34-36 weeks, so-called “late” preterm infants, according to a study by a National Institutes of Health research network.

Steroids are a standard treatment for women likely to deliver before 34 weeks of pregnancy because these drugs are known to reduce respiratory and other complications, as well as death, among infants born early preterm. Now, researchers have found that steroids also reduce the occurrence of serious respiratory complications in late preterm infants.

Previously, it was believed that late preterm infants could thrive without their mothers having received steroid treatment. Researchers then learned that late preterm infants have a higher risk of respiratory complications compared to infants born at 37 weeks or later.

“Eight percent of all deliveries occur in the late preterm period,” said study author Uma Reddy, M.D., M.P.H., of the Pregnancy and Perinatology Research Branch at the NIH’s Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD). “Our results indicate that prenatal steroid therapy for women delivering late preterm could greatly reduce the rate of serious respiratory complications in this group of infants.”

The study was co-funded by NICHD and the National Heart, Lung and Blood Institute (NHLBI).

“Reducing neonatal respiratory complications could result in less injury to the immature lung, less hospitalizations, earlier infant-mom bonding, and better long-term lung and general health,” said Carol Blaisdell, MD, NHLBI medical officer and program officer for the study.

Women who participated in the study were in the 34th through the 36th week of their pregnancies, and at high risk for delivering early (before 37 weeks).The researchers randomly assigned 2,831 participants to receive two injections of the steroid betamethasone or a placebo, 24 hours apart.

The researchers categorized the study findings into a single composite measure, a primary outcome derived from the need for any of a number of therapies used to treat difficulty in breathing in the newborns, including:

Continuous positive airway pressure (CPAP), use of mild air pressure, so that sufficient air can reach the lungs;

Oxygen therapy, in which oxygen at concentrations higher than that in room air is passed into the baby’s lungs;

Mechanical ventilation, in which a tube is placed in the infant’s windpipe and used to deliver oxygen to the infant’s lungs.

Also included in the primary outcome was whether an infant was stillborn or died before 72 hours of age.

At the study’s conclusion, 11.6 per cent of the infants in the betamethasone group met the criteria for the primary outcome — a 20 per cent reduction in the need for respiratory support by 72 hours of age, compared to the placebo group. Two infants in the betamethasone group died before 72 hours, but these deaths were not from respiratory causes. One infant died from a heart defect, and the other from sepsis, a blood infection that frequently occurs in preterm infants. The rate of sepsis (a serious blood infection) was roughly the same for both groups.

The researchers also evaluated the infants according to several secondary outcomes. The first of these, severe respiratory illness, included the need for CPAP therapy or supplemental oxygen for at least 12 continuous hours, a high concentration of oxygen for at least 24 hours, or mechanical ventilation. Again, the betamethasone group fared better, with 8.1 per cent qualifying for this secondary outcome — a 33 percent reduction in serious respiratory illness compared to the placebo group. Infants in the betamethasone group also were less likely to experience transient tachypnea (fluid in the lungs) or bronchopulmonary dysplasia — tissue damage and scarring that may accompany oxygen or ventilator therapy.

Infants in the betamethasone group were more likely to have low blood sugar than those in the placebo group (24 per cent vs. 14.9 per cent). Therefore, the data support the monitoring of neonatal blood sugar levels when steroids are given in this situation.  Overall, betamethasone administration for women at risk for late preterm delivery decreased the rate of respiratory complications in their infants. Although the drug increased the risk of low blood sugar in the infants, there were no other differences in complication rates between infants or their mothers.

The NICHD sponsors research on development, before and after birth; maternal, child, and family health; reproductive biology and population issues; and medical rehabilitation.