Maternal Factors, Treatment Interventions Associated With Hypothermia in Premature Newborns

Katherine A. Kahn, DVM

October 13, 2008

October 13, 2008 (Boston, Massachusetts) — Certain maternal factors, such as illicit drug use and neonate intensive-care interventions (including positive-pressure ventilation), are associated with hypothermia in premature newborns, a new study reveals. Other factors, such as cardiopulmonary resuscitation (CPR) and prolonged delivery-room time are not associated with hypothermia. Principle investigator Lilian St. John, MD, from the University of Texas Southwestern Medical Center of Dallas, presented the results here at the American Academy of Pediatrics 2008 National Conference and Exhibition.

"Hypothermia has been an issue plaguing neonatology since the 1900s," Dr. St. John told Medscape Pediatrics. "Several studies have demonstrated increased mortality among preterm newborns who are hypothermic. We wanted to determine if there were specific maternal or infant aspects that might identify at-risk neonates." The study authors also wanted to determine whether delivery-room resuscitation efforts might contribute to hypothermia in preterm neonates.

The study included all neonates who were 34 weeks obstetrical estimated gestational age (OB EGA) or less born between January 1, 2003 and November 30, 2007 at the Parkland Memorial Hospital in Dallas. Researchers excluded infants who were nonviable, transferred from other nurseries, or had missed critical data points. Of the 2183 newborns included in the study, more than half were hypothermic, defined as a rectal temperature of less than 36.5 °C. Euthermia was defined as a rectal temperature of 36.5 °C to 37.5 °C. "We found that 54% of our [preterm] babies were becoming cold, so that was alarming to us," Dr. St. John told Medscape Pediatrics.

Researchers found that maternal illicit drug use and pre-eclampsia were associated with a significantly increased risk for hypothermia in preterm neonates. In hypothermic preterm neonates, 4.2% of mothers reported illicit drug use, compared with 2.5% of euthermic neonates (P = .04). Maternal pre-eclampsia occurred in 33% of hypothermic neonates and in 17% of euthermic neonates (P < .001). Dr. St. John speculated that both these factors could result in decreased circulation in the neonate, leading to hypothermia.

Maternal steroid use, antibiotic use, chorioamnionitis, and premature rupture of membranes (PROM) were associated with decreased risk for hypothermia, researchers found. In hypothermic neonates, maternal steroid use occurred in 19%, whereas in euthermic neonates, maternal steroid use occurred in 25% (P < .001). "We presumed this was from an improvement in maturation of thermal capabilities in the neonate as a direct result of antenatal steroids," Dr. St. John said. Antibiotic use, chorioamnionitis, and PROM were found to be protective against hypothermia, primarily because of hyperthermia associated with infection in these circumstances, she added.

Parker L. Simon, DO, MPH, commented on the apparent decreased risk for hypothermia with maternal steroid use. "We don't have the data to say that [maternal] steroids are protective against hypothermia in the preterm neonate. The apparent effect is probably multifactorial." Dr. Simon is a research fellow from the division of neonatal-perinatal medicine at the University of Oklahoma, in Oklahoma City, and a conference attendee and presenter.

The study also examined infant characteristics and the development of hypothermia. Preterm neonates with lower birth weight, intrauterine growth restriction, and breech presentation were more likely to be hypothermic.

Researchers also examined the use of resuscitation and delivery-room characteristics. As expected, the use of occlusive wrap and sodium-acetate-gel mattresses led to lower percentages of neonates with hypothermia. Of hypothermic neonates, 85% who were 28 weeks OB EGA or younger underwent positive-pressure ventilation or intubation, whereas only 76% of euthermic neonates underwent these procedures (P = .04), suggesting an increased risk for hypothermia with these procedures. "This is likely due to the fact that we use cold unhumidified air," Dr. St. John said. "It's certainly possible that using warm humidified air would help." Hypothermia was also associated with more ventilator days in neonates in both the 28-week and 34-week cohorts; however, it was not associated with CPR or prolonged time in the delivery room.

When asked what measures can help decrease the risk for hypothermia, Dr. St. John stressed the importance of using occlusive wraps and sodium-acetate-gel pads. "We also need to be keeping the hospital environment warmer," she added.

Dr. Simon concurred. "Part of the solution to this problem is getting the obstetrics staff on board — ambient room temperature in the operating room when C-sections are performed may only be 66 °[F]," he said. "Also, although occlusive wrap and sodium-acetate-gel mattresses have similar efficacy, there could be situations when it's best to use both. These are cost-effective measures."

The study was internally funded, and the authors have disclosed no relevant financial relationships.

American Academy of Pediatrics (AAP) 2008 National Conference and Exhibition: Poster 20. Presented October 10, 2008.

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