The peripheral temperature generated by skin and skeletal muscle is often lower than the core temperature, and so helps to regulate the core temperature by assisting with heat loss and gain. Peripheral temperatures reduce proportionally as distances increase from the core.

Different body sites have different normal values. These are usually determined according to the nearness of the site to a major blood vessel and the route that it is taking to/from the heart. According to Dubois (1948), the normal oral temperature is set within a range of 35.8–37.3°C; however, everyone has their own ‘normal’ oral temperature setting within this range. Thus, a rise in core temperature of 1°C may be difficult to detect if a person’s normal oral temperature is 36.0°C.

Circadian rhythms influence both the core and the peripheral temperature. Body temperature is lowest during the night and peaks in the evening.

Body temperature is lower during the postmenstrual period of the menstrual cycle, increasing by 0.3–0.5°C after ovulation. This rise in body temperature is maintained until progesterone levels decrease prior to the onset of menstruation (Hinchliff et al., 1996 and Houdas and Ring, 1982).

A slight increase in temperature of 0.1–0.2°C has been noted to occur with normal digestion.

Heat is produced as a result of chemical reactions within the body. When the body is at rest, this is referred to as the basal metabolic rate (BMR). The amount of heat produced can be altered by various regulatory mechanisms to ensure the body temperature is maintained within the normal range: the higher the BMR, the more heat is produced, the higher the temperature (Houdas & Ring 1982). BMR decreases with age, thus babies have a higher BMR than adults; also, women have a slightly lower BMR than men (Chinyanga 1991). Certain diseases/disorders will increase the BMR (e.g. hyperthyroidism). Exercise can also cause a rise in temperature; Closs (1987) suggests that strenuous exercise might increase the core temperature to 40°C.

These can raise the body temperature by 0.5–1.0°C for up to 45 minutes.

Leucocytes release endogenous pyrogens in response to stimulation by pyrogenic substances such as bacterial, viral and protozoal infection and necrotic tissue. This causes the thermostat within the hypothalamus to be ‘reset’ at a higher level. The affected person feels cold and the body attempts to raise the temperature to maintain it within its higher ‘normal’ range. When the level of endogenous pyrogens decreases, the thermostat returns to its original setting. The person then feels hot, with the body attempting to lower the temperature to its normal setting.

The drugs used during general anaesthesia can interfere with the normal homeothermic mechanisms that assist with heat loss and gain, predisposing to heat loss (Schönbaum & Lomax 1991). Chinyanga (1991) proposes that the greatest decrease in body temperature will occur during the first hour of anaesthesia and that this can induce postanaesthetic shivering.

Kalant and Lé (1991) conclude from their review of the literature that large amounts of alcohol will lower the body temperature.

This is discussed in detail below.

During pregnancy, progesterone and a raised metabolic rate increase the amount of heat generated by 30–35%. Although the body attempts to compensate for this by increasing heat loss mechanisms, the maternal temperature can increase by 0.5°C (Blackburn 2007).

Intrauterine temperature is determined partly by maternal temperature and partly by the maternal–fetal gradient, as the fetus is unable to regulate its own temperature. Generally, the fetal temperature is approximately 0.8°C higher than the maternal oral temperature (Banerjee et al 2004). Therefore, a raised maternal body temperature will result in a higher fetal temperature and is associated with intrauterine hypoxia, fetal tachycardia, teratogenesis and preterm labour (Blackburn 2007).

During labour, a rise in temperature can be indicative of infection, dehydration or the result of increased muscular activity from uterine contractions. It is often associated with the use of epidural analgesia.

A transient rise in maternal temperature can occur within the first 24 hours after delivery; it might result from the stress of labour and be related to dehydration. Blackburn (2007) suggests that up to 6.5% of women have a rise in temperature to 38°C in the 24 hours following a vaginal birth. In the majority of cases, this is physiological and resolves spontaneously. However, for a small number of women, the temperature rise could be due to an infection, such as a puerperal infection, mastitis or a urinary tract infection, or might result from an inflammatory process, such as the development of a deep venous thrombosis. The temperature may also rise in breastfeeding women around the second to third day as milk production occurs. This will resolve spontaneously once lactation is established although it can take several days.

Consequently, babies lose heat by evaporation, especially before thorough drying, by convection when draughts blow over them, by radiation and conduction to nearby items and surfaces. A decrease in temperature of between 1 and 2°C might occur during the first hour after birth. If action is not taken to remedy this, a normal body temperature may not be achieved for 4–8 hours afterwards (Black 1972). Various measures can be taken at birth to protect the baby’s temperature. The World Health Organization (WHO 1997) calls this ‘the warm chain’ (consideration to room temperature, immediate drying, postponing weighing and bathing, etc.), and skin-to-skin contact has value for both temperature regulation and breastfeeding success.

Heat production comes mainly from metabolic processes, moving and shivering both being limited activities. External clothing helps, while the stores of brown fat are utilised, along with calories from milk. Metabolism requires both glucose and oxygen; a cold baby rapidly becomes hypoxic and hypoglycaemic and can have a serious metabolic acidosis. The problems are compounded significantly if the baby is preterm or small for gestational age.

Attention to careful management of the baby’s temperature immediately following birth and in the first weeks of postnatal life is essential, including education of the parents. Danger exists for hyperthermia as well as hypothermia. An infected baby may display a changeable or cool temperature rather than the expected high temperature.

As stated above, temperature may be recorded if other observations suggest a deviation from the norm. What the woman looks like (e.g. hot, pale, flushed, sweaty) and how she is feeling or behaving also add to the observation. Although midwives offer individualised care to women and babies based on their needs, there are circumstances when routine temperature measurement is required, for example, 4-hourly in labour (NICE 2007). The value of a baseline recording (particularly prior to surgery) is a means of ensuring that deviations from the norm for that woman are quickly noticed and acted upon. Other likely indications are: