The use of thermography in placenta location during pregnancy
The placenta location is relevant for both the mother’s and baby’s health. It is usually attached to the top, front, or back of the uterus, but it can also be attached to the bottom, which may mean an eventual risk. As in a recent post, we learned how we can detect the position of the fetus. The placenta is the second essential intrauterine structure developed during pregnancy that needs to be monitored.
Main imaging techniques used for placenta analysis
The placenta is the organ that provides oxygen and nutrients to a growing baby in the uterus during pregnancy. Many imaging techniques have been used in the last 50 years, because several medical disorders of the pregnant woman or her fetus begin or end in the placenta, such as pre-eclampsia, and other forms of hypertension in pregnancy, less than optimal fetal growth (i.e. intrauterine growth restriction), triploidy (and its placental manifestation: partial mole), non-immune hydrops as well as several infectious processes (Abramowicz J. S., & Sheiner E., 2007).
“Furthermore, Infrared Thermography is both non-contact and non-invasive, so may be an optimal tool in maternal and neonatal care, but not the only one.”(Topalidou et al. 2020)
Some of the methods that are used to establish the location of the placenta require exposing the mother and fetus to ionizing radiation. For this reason, there are some less invasive methods that investigate the position of the placenta during pregnancy. Furthermore, Infrared Thermography is both non-contact and non-invasive, so maybe an optimal tool in maternal and neonatal care, but not the only one (Topalidou et al. 2020). Therefore, Young et al. (1964) claim its use as it is quick, simple, and completely harmless to both mother and fetus.
The placenta throughout thermography analysis
It has been shown in different investigations since the ’60s, that the temperature of both the placenta and the fetus is around 0.5ºC higher, compared to the maternal core temperature (Walker et al. 1969; Gilbert et al. 1985).
The main explanation is based on the hypothesis that ”the placenta, being an arteriovenous fistula, has a higher temperature than its immediate environment, and the heat from this area is transmitted through the adjacent anterior abdominal wall to produce a characteristic pattern of heat emission on its surface” (Millar et al. 1966). This measure can be affected by the thickness of the wall of the uterus in obese patients, as Young et al. (1964) found out.
So for this reason, using non-invasive methods, such as thermography, seem to be a good option. One of the methods that have been used to identify the location of the placenta is “Liquid Crystal Thermography”. This method was used by Liu & Blackwell (1980) and is based on a liquid mixture that is applied to the abdominal surface. It shows a color variation for every 0.5º C change, in a range from 36º C to 40º C. The color change first progresses from red to yellow, then from green to blue at the top of the range. The abdominal surface is usually divided into seven regions, as showed in figure 1, and the liquid crystal plate is placed over those sites. In order to assign the placenta to a particular location, the color change had to fulfill at least half of the designated area with an intense blue.
The use of this method supported the findings of Peterson et al. (1971), where they claimed an 80% probability of correctly identifying placenta location in patients with advanced pregnancies by using liquid crystal thermography.
Advantages and disadvantages of the use of thermoplacentography
On the one hand, Johnson et al. (1966), as can be seen in figure 2, compared the radiopharmaceutic and thermographic methods to establish the location of the placenta. They found out that the advantages of thermoplacentography is that it avoids radiation to both the fetus and the mother. However, the disadvantages of this method are the high prices, the need for separate physical facilities, and the introduction of thermographic artefacts from the motion of the patients, especially during the discomfort of uterine contractions.
Due to the lack of accuracy in placenta location, other methods, such as ultrasound, are needed to not only confirm what thermography shows, but also to analyze the placental structure and its function. Besides, thermography can help evaluate specific placental conditions, such as abnormal placentation (placenta previa and accreta for instance), gestational trophoblastic disease and placental tumors (e.g. chorioangioma). (Abramowicz J. S., & Sheiner E., 2007)
To sum up, most of the methods that have been used to analyze placenta location are contraindicated in pregnant humans and have essentially been replaced by harmless techniques, such as ultrasound or thermography, as they are non-invasive. The thermographic examination has been attempted by a number of investigators with varying degrees of success and it seems that there are differences of opinion among authors as to the accuracy of this method of examination, so further research is needed.
Abramowicz, J. S., & Sheiner, E. (2007). In utero imaging of the placenta: importance for diseases of pregnancy. Placenta, 28, S14-S22.
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.
Johnson, P. M., Bragg, D. G., & Sciarra, J. J. (1966). Placental localization: a comparison of radiopharmaceutic and thermographic methods. American Journal of Roentgenology, 96(3), 681-689.
Millar, K. G. (1966). Placental localization by thermography. British Medical Journal, 1(5503), 1571.
Liu, D. T. Y., & Blackwell, R. J. (1980). Placental localization by liquid crystal thermography. International Journal of Gynecology & Obstetrics, 17(6), 617-619.
Peterson, E. N., Dixon, G. D., & Levine, M. A. (1971). Placental localization by liquid crystal thermography. Obstetrics & Gynecology, 37(3), 468-473.
Topalidou, A., Markarian, G., & Downe, S. (2020). Thermal imaging of the fetus: An empirical feasibility study. PloS one, 15(7), e0226755.
Young, R. J. (1964). Application of thermography to the problem of placental localization: preliminary communication. British Medical Journal, 2(5415), 976-4.
Walker, D., Walker, A., & Wood, C. (1969). Temperature of the human fetus. BJOG: An International Journal of Obstetrics & Gynaecology, 76(6), 503-511.
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