Thermography as a tool to assess the position of the fetus
Can thermography be used to follow the fetus position during a woman’s pregnancy? Today we will answer this question, giving examples of real pregnant women and its thermal correlation with the fetus position.
The uterus provides a relatively stable thermal environment where the fetuses develop due to the appropriate constant supplies of heat to the amnion via the placental surface and the umbilical circulation of the maternal body. (Asakura., 2004)
Most of the studies in this field are done with animals, so further investigation with humans is needed.
FETAL HEAT PRODUCTION
During the development of the fetus in the uterus, the fetus is warmed by its own metabolic processes. There have been two ways to know this, by measuring heat production of fetal sheep, discovering 47 calories per minute per unit of body weight, which is approximately twice an adult’s heat production per unit of body weight (Power et al., 1984). On the other hand, by measuring oxygen consumption, they found out that the fetal lamb was 1,5 higher than an adult lamb with 6,7ml/kg/min of O2 (Asakura et al., 1990), indicating that the basal metabolic rate of the fetus is higher than that of an adult, resulting in significant fetal heat being produced. Due to this increase, the fetal temperature constantly remains 0.3º C to 0.5º C higher than an adult (Power et al., 1984). It is also remarkable that the heat produced by the fetus is transferred to the mother.
THERMOGRAPHY AND DISSIPATION OF FETAL HEAT TO THE MOTHER
Gilbert et al. (1985) found out that 85% of the heat produced by fetal lamb is transferred to the mother via the umbilical circulation and the remaining 15% was dissipated through the fetal skin to the amnion, and then passed through the uterine wall and to the maternal abdomen.
By using tele-thermography, they found out that fetal temperatures rapidly changed in response to a disturbance in umbilical blood flow, such as the coiled of the umbilical cord, which increased the skin temperature of a newborn human shortly after birth, because heat accumulates within the fetus (Asakura H., 1996). For this reason, the fetal temperature is maternally dependent until birth.
THERMOGRAPHY AND NON SHIVERING THERMOGENESIS
Oya et al. (1997) used thermography to measure the extent of non-shivering thermogenesis (NST) in brown adipose tissue of human newborns receiving routine thermal care and examine the influence of oxygen level at birth on the initiation of NST. They found out that NST is initiated within minutes of birth and contributes to the elevation of body temperature and is reduced by low arterial PO2 at the moment of birth.
THERMOGRAPHY AND FETAL POSITION
Thermography is also used to record fetal presentation and position, and other pregnancy-related physiological factors, via their superficial thermal prints, due to not requiring direct contact and since it is completely non-invasive. Topalidou A., et al. (2020) found out that thermography can identify the position of the fetus if it is in cephalic position compared to anterior view and fetal movements influenced the thermal patterns that were produced. In figure 1, you can see thermal images from the viewpoint of the pregnant belly with three different positions of the fetus.
Moreover, Varsier N., et al (2014) analyzed the influence of pregnancy stage and fetus position on the whole body. From the 15 to 41 weeks of amenorrhea (WA), the large majority of fetuses are in the vertical position, where 40 to 90% are with the head down and up to 20% are head up. Showing that until the end of the second pregnancy trimester, the fetus can be in breech, transverse or oblique position which is more unlikely to happen at the last stage (See figure 2).
This is important because the position of the baby before delivery and especially during childbirth is related to the increased risk of neonatal mortality (NNM), a vaginal breech delivery, regardless of whether planned or actual, and actual breech cesarean delivery were associated with excess risk for NNM compared with vaginal cephalic delivery (Bjellmo, S. 2017). The risk factor for parturition in breech presentation is elevated (OR = 2.98 and p <0.05) (Vilchez Agruta, E. C. 2015).
To sum up, thermography shows that it can be used to detect physiological conditions, alterations related to pregnancy and to fetal factors, as well as to record maternal-fetal dynamic interaction in pregnancy. Pregnant women rated the idea of using thermography in research and clinical practice very highly.
Knowing the position of the fetus during pregnancy and especially in the final stages before delivery can be interesting to manage the risks associated with childbirth.
Asakura, H. (1996). Thermogenesis in fetus and neonate. J Nippon Med Sch, 63, 171-172.
Asakura, H. (2004). Fetal and neonatal thermoregulation. Journal of Nippon Medical School, 71(6), 360-370.
Asakura, H., Ball, K. T., & Power, G. G. (1990). Interdependence of arterial PO2 and O2 consumption in the fetal sheep. Journal of developmental physiology, 13(4), 205-213.
Gilbert, R. D., Schroder, H., Kawamura, T., Dale, P. S., & Power, G. G. (1985). Heat transfer pathways between fetal lamb and ewe. Journal of Applied Physiology, 59(2), 634-638.
Oya, A., Asakura, H., Koshino, T., & Araki, T. (1997). Thermographic demonstration of nonshivering thermogenesis in human newborns after birth: its relation to umbilical gases.
Power, G. G., Schroder, H., & Gilbert, R. D. (1984). Measurement of fetal heat production using differential calorimetry. Journal of Applied Physiology, 57(3), 917-922.
Varsier, N., Dahdouh, S., Serrurier, A., De la Plata, J. P., Anquez, J., Angelini, E. D., … & Wiart, J. (2014). Influence of pregnancy stage and fetus position on the whole-body and local exposure of the fetus to RF-EMF. Physics in Medicine & Biology, 59(17), 4913.
Vilchez Agruta, E. C. (2015). Tasa y factores de riesgo de la mortalidad fetal en el Hospital Hipólito Unanue de Tacna durante los años 2009–2013.
Bjellmo, S., Andersen, G. L., Martinussen, M. P., Romundstad, P. R., Hjelle, S., Moster, D., & Vik, T. (2017). Is vaginal breech delivery associated with higher risk for perinatal death and cerebral palsy compared with vaginal cephalic birth? Registry-based cohort study in Norway. BMJ open, 7(4), e014979.
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