Special Feature: What is the Best Way to Monitor Maternal Temperature in Labor?

By John C. Hobbins

To answer the above question a team of british investigators (Banerjee S, et al. Obstet Gynecol. 2004;103:287-293) inserted an intrauterine temperature sensor in 18 laboring patients with epidural anesthesia at the time they were inserting intrauterine pressure catheters. These patients then were monitored with periodic oral thermometer sampling, continuous skin temp assessment (taped to the inner thigh) and the commonly used ear canal temperature assessments.

Banerjee et al Found:

  1. Intrauterine temperatures rose on average throughout labor (average at a rate of 0.04ºC per hour);
  2. The average intrauterine temperature was 38.1ºC in this group, compared with previous studies in which temps varied between 36º and 37º C in patients without epidural.
  3. Most important, the oral temperature was the most consistent predictor of intrauterine temperature, undershooting on average by 0.8ºC.

It is clear from this study that oral temperatures reasonably reflect intrauterine temperature (with a sensitivity of more than 80% and a specificity of 96%) once one adds 0.8ºC to the reading. The study also shows that skin temperature assessments, theoretically representing vasodilation and ear canal methods to reflect tympanic membrane temperature, are poor indicators of maternal core temperature.

That said—how important is it to accurately predict the intrauterine temperature? Data from recent investigation in humans and in personal models suggest the following:

  1. fetal core temperature is about 0.5ºC higher than intrauterine temperature;
  2. an increase in fetal brain temperature even in the absence of infection has an additive effect in brain damage from fetal hypoxia/ischemia;
  3. increases in maternal temperature, grossly reflecting many etiologies, is associated with many adverse pregnancy outcomes;
  4. epidural does seem to elevated maternal core temperature.

So from the above "true and maybe related," it seems reasonable to keep track of maternal temperature at frequent intervals, and if one excludes intrauterine temperature assessments as being invasive and maternal rectal thermometer assessment as being intrusive (as one patient survey has shown), then, let’s say, hourly oral temp taking could suffice.

Last, one of the earliest clues of increasing maternal core temperature in labor is a fetal tachycardia. Elevation in baseline fetal heart rate is generally not an indirect reflection of fetal infection but simply represents how poorly equipped the fetus is to dissipate heat without the usual mechanisms that infants possess. However, heat by itself may represent potential trouble for the fetus and should be monitored carefully.

 John C. Hobbins, MD, Professor and Chief of Obstetrics, University of Colorado Health Sciences Center, Denver is An Associate editor for OB/GYN Clinical Alert.

Suggested Reading

1. Wass CT, et al. Anesthesiology. 1995;83:325-335.
2. Dietrich WD, et al. Stroke. 1990;21:1318-1325.
3. Lieberman E, et al. Pediatrics. 2000;105:8-13.
4. Lieberman E, et al. Pediatrics. 2000;106:983-988.