Effects of heat on embryos and foetuses

Abstract

Hyperthermia during pregnancy can cause embryonic death, abortion, growth retardation and developmental defects. Processes critical to embryonic development, such as cell proliferation, migration, differentiation and programmed cell death (apoptosis) are adversely affected by elevated maternal temperatures, showing some similarity to the effects of ionizing radiation. The development of the central nervous system is especially susceptible: a 2.5 degrees C elevation for 1 h during early neural tube closure in rats resulted in an increased incidence of cranio-facial defects, and a 'spike' temperature elevation of 2-2.5 degrees C in an exposure of 1 h during early neurogenesis in guinea pigs caused an increase in the incidence of microencephaly. However, in general, thresholds and dose-response relationships vary between species and even between different strains of the same species, depending on genotype. This precludes rigorous quantitative extrapolation to humans, although some general principles can be inferred. In humans, epidemiological studies suggest that an elevation of maternal body temperature by 2 degrees C for at least 24 h during fever can cause a range of developmental defects, but there is little information on thresholds for shorter exposures. Further experimental and epidemiological studies are recommended, focusing on stage-specific developmental effects in the central nervous system using a variety of sensitive assays.

Fever in pregnancy and its maternal and fetal outcomes

“…3 Cotch and associates observed an increased incidence of preterm labor in neonates, of women with chorioamnionitis (30%). 2 The observed incidence for these complications was much lower in our study, as compared to that quoted in literature.…”

The Sensitivity of Children to Electromagnetic Fields

“…The heat produced by fetal metabolism is dissipated to the mother mostly at the placenta, but this is less efficient than expected and the temperature of the fetus is usually ϳ0.5°C above that of the mother. 47 The difference between the ability of children and that of adults to dissipate whole-body heat loads is small. During exercise in thermally neutral or warm environments, children thermoregulate as effectively as adults.…”

“…47 In humans, epidemiologic studies suggest that an elevation of maternal body temperature by 2°C for at least 24 hours during fever can cause a range of developmental defects, although a causal relationship has not been established. In addition, young infants aged 2 to 3 months are even more vulnerable than neonates because of their higher metabolic rate, better tissue insulation, and slightly lower surface area/mass ratio.…”

Synaptic organization in the adult honey bee brain is influenced by brood-temperature control during pupal development

“…In lower vertebrates, temperature manipulations during embryonic development affect sex determination and adult aggressive behavior, most likely mediated by changes in sexually dimorphic brain nuclei (18,19). In mammals, slight temperature increases during embryonic development were shown to have profound effects on the nervous system (20).…”