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Control of Thermoregulation

Thermal homeostasis is controlled by the hypothalamus within a range of 36.5°C to 38°C. Fever is defined as a temperature greater than 38°C and is caused by resetting the thermoregulatory threshold of the hypothalamus (eg, by pyrogens released in response to infection), deregulation of heat production (eg, malignant hyperthermia), or dissipation. See Figure 18-1 for a schematic view of thermoregulation.

Figure 18-1.

Schematic representation of thermoregulation.

Causes of Fever in Pregnancy

There is a broad differential diagnosis for fever in the parturient, including infective and noninfective causes, which may or may not be directly related to the pregnancy (Table 18-1). Infective disease patterns, incidences, and outcomes vary significantly between more-developed and less-developed regions of the world.

Table 18-1.Causes of Fever in Pregnancy

Predisposition to Infection

Parturients are predisposed to infection for several reasons. These may be physiologic. Parturients may develop relative immunosuppression in order to tolerate fetal alloantigens and prevent fetal compromise and demise.1,2 A pH change in vaginal epithelium may alter the environment for microorganism growth.1 Alternatively, the reasons may be anatomic. Urinary tract dilation and urinary stasis, from a gravid uterus and progesterone, are risk factors for urinary tract infection (UTI).1,2 Increased intra-abdominal pressure and upward diaphragm displacement by a gravid uterus increases basal atelectasis, potentially predisposing to pneumonia.1

Peripartum, there are additional risk factors:

  • Premature rupture of membranes (PROM)

  • Labor dystocia: prolonged labor and repeated vaginal examinations

  • Use of immunosuppressive drugs (eg, steroids for preterm labor)

  • Interventions, such as urinary catheterization

Consequences of Fever in Pregnancy

Maternal consequences include increased oxygen demand, increased use of antibiotics, increased assisted delivery rate, and increased cesarean delivery rate. Fetal consequences include increased oxygen demand, increased screening for sepsis,3 increased use of prophylactic antibiotics,3 admission to neonatal intensive care with separation from mother,3 and possible increased incidence of hypoxic encephalopathy.3,4

Fetal temperature is dependent on maternal temperature and is commonly 0.5°C higher than maternal.2 If maternal fever is infective in origin, ...

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