Causes of Fetal Hypothermia
Fetal hypothermia is primarily caused by maternal hypothermia, inadequate thermoregulation mechanisms, and placental insufficiency, all of which can significantly increase neonatal mortality and morbidity. 1, 2
Maternal Factors
- Maternal hypothermia: When the mother's core temperature drops below normal, the fetus is directly affected since fetal temperature is typically 0.3-0.5°C higher than maternal temperature 3
- Inadequate operating room temperature: Operating room temperatures below 21-25°C during cesarean delivery can contribute to both maternal and fetal hypothermia 1
- Prolonged labor: Extended labor in cold environments can lead to maternal hypothermia that transfers to the fetus 4
- Maternal medications: Certain medications that affect maternal thermoregulation can indirectly cause fetal hypothermia
Placental and Umbilical Factors
- Placental insufficiency: Compromised placental function reduces heat transfer to the fetus 5
- Umbilical cord compression: Partial occlusion of umbilical circulation disrupts the normal heat transfer from mother to fetus 3
- Reduced placental blood flow: Any condition that decreases uteroplacental perfusion can reduce heat transfer to the fetus
Fetal Factors
- Inability to generate heat: The fetus cannot produce extra heat through non-shivering thermogenesis (NST) due to placental inhibitors like adenosine and prostaglandin E2 3
- Fetal distress and hypoxemia: A distressed fetus with inadequate oxygenation cannot produce sufficient heat 3
- Intrauterine growth restriction: Growth-restricted fetuses have less brown adipose tissue and impaired thermoregulation
Environmental Factors
- Amniotic fluid temperature: Cold amniotic fluid can directly affect fetal temperature
- Iatrogenic causes: Medical interventions like amnioinfusion with room-temperature fluids can induce fetal hypothermia
Clinical Implications
Fetal hypothermia is associated with serious complications including:
- Increased mortality risk 1, 2
- Respiratory distress syndrome 2
- Metabolic disorders including hypoglycemia 1, 2
- Intracranial hemorrhage 2
- Increased risk of late-onset sepsis 2
Prevention Strategies
- Maintain maternal normothermia during labor and delivery 1
- Ensure appropriate operating room temperature (21-25°C) during cesarean delivery 1
- Use warming methods during cesarean delivery including forced air warming and intravenous fluid warming 1
- Monitor maternal temperature regularly during labor and delivery 1
Management
For newborns with hypothermia:
- Immediate drying and covering of the infant's head to reduce heat loss 1
- Skin-to-skin contact or kangaroo mother care 1
- Use of exothermic heaters, transwarmer mattresses, plastic wraps/bags for preterm infants 1
- Maintain body temperature between 36.5°C and 37.5°C after birth 1
Important Caveats
- Rapid rewarming of hypothermic newborns may lead to complications such as apnea and arrhythmias, though evidence is insufficient to recommend either rapid (≥0.5°C/h) or slow (<0.5°C/h) rewarming 1
- Hyperthermia (>38.0°C) should be avoided due to potential associated risks 1
- Preterm infants are especially vulnerable to hypothermia and require more aggressive prevention measures 1
Understanding these causes and implementing appropriate preventive strategies can significantly reduce the incidence of fetal hypothermia and its associated complications.