In 1910 every 8th child died during delivery (12.5 %), in 1949 still 4.9 % (BRD) died, since then the rate of infant perinatal (time from delivery until seven days later) mortality has dropped continuously down to about 0.6 % (Germany 1999). These deaths are nowadays only very seldomly caused by the conduct of midwives, physicians or expectant mothers during delivery. These deaths can mostly be attributed to diseases not compatible with life outside the uterus or to extremely premature birth. Many changes, both medical and common social ones, have contributed to this improvement.

Today the percentage of babies suffering brain damage caused by hypoxia (oxygen deficiency) is higher than the percentage of perinatal mortalities. Perinatal lack of oxygen still represents one of the greatest threats to the unborn child during delivery.
With increasing survival chances of children, parents increasingly expect their infants to be healthy at birth. This has not remained without consequences: anxious about their baby's well-being, an increasing number of women requests a Caesarean section without ever having tried a natural, vaginal delivery. In fear of growing liability consequences for the obstetrician, there is also among physicians an increasing readiness to decide in favor of a Caesarean section in case of doubt. There­fore the Caesarean section rate has dramatically increased worldwide, in Germany from 3.6 % (1949) to 18.6 % (1999), in our European neighboring countries to over 20 %, in the USA partly to over 30 %, in Brazil to over 70 %.

Es wurden und werden erhebliche Mittel (erfolgreich!) aufgewandt für Vorsorge­pro­gramme zur Überwachung von Müttern und Kindern in der Schwangerschaft. Allein die entscheidende Phase unserer Mensch­werdung, die Geburt selbst, wird noch immer mit einer Methode überwacht, welche schon zu Lebzeiten Napoleons (Paris 1818) gefunden wurde. Damals fanden zwei Forscher nahezu gleichzeitig, dass die fetale Herzfrequenz gewisse Rückschlüsse auf den Zustand von Kindern unter der Geburt erlaubt. Die Messung der fetalen Herz­frequenz ist in allen Industrienationen noch immer das wichtigste und nahezu aus­schließliche Über­wachungs­instru­ment zur Messung des kind­lichen Zustan­des unter der Geburt.
Despite the technical progress in the form of an intermittently used ear trumpet to the CTG which monitors every single heart beat, we are still far from making reliable statements about fetal well-being during delivery. The Cardiotocogram (the monitoring of the fetal heart rate together with uterine contractions) does not show the true state of health of the unborn. The fetal heart rate can depend on a variety of factors, e.g. on stimulations of the nervus vagus (autonomic nerve), on the compression of the little fetal head in the birth channel, on catecholamines in the fetal or maternal circulation produced by the stress of the delivery, on the position of the mother, on stress in her circulatory system, on drugs given to make the delivery less painful and on other factors. Thus, according to newer investigations, less than 20 % of pathological fetal heart rate patterns correlate with a true threat to the fetus, resulting in many unnec­essary Caesarean sections (Lit.: Göschen 1984, Göschen 1992 / Diemer u. Beck, Der Gynäkologe, S.187-190, 1992 / Gross W. Jahrbuch der Gynäkologie und Geburtshilfe S. 77-89, 1991 / Visser G.H.A. Bailleres Clinical Obstetrics and Gynecology, S. 117-124, Bd. 1, 1988).

This has resulted in worldwide efforts to find additional parameters which allow researchers to draw better conclusions concerning fetal well-being. Simultaneously efforts have been made to gain access to these parameters during delivery with as minimal an intervention as possible in the progress of the delivery, while nonetheless providing access to these parameters as often as possible - continuous access would be ideal. Among these parameters are the pH-value of the blood, the lactate content, the base excess, flow conditions in maternal (uterus) and fetal blood vessels (umbilical cord arteries, meningeal arteries). All these parameters, however, are only quite indirect in­dicators of true fetal well being and are subject to falsifying influences and factors.

Saling (1961) introduced micro blood analysis as a method of allowing a better diagnosis of the fetal health status using the pH-value. Despite the fact that this technique signifi­cantly improved fetal diagnostics, the micro blood analysis is used only reluctantly. This drawback of the MBA has to do with the technical complexity of this method. It is difficult to perform, traumatizing for the fetus and therefore cannot be repeated ad lib.
The continuous monitoring of the pH-value has up to now not reached clinical feasibility. (Stamm 1976, Bloch 1978, Lauersen 1979, Small 1989).

The Doppler-sonographic investigations of uterine and fetal vessels can lead to prognos­tic results during pregnancy (overview in Beck L., Bender H.G., Hepp H., Künzel W. (Editors), Der Gynäkologe, Issue 5/92, Springer Verlag). However, at present, flow measurements are not suitable for the diagnosis of fetal well-being (Weiss E., Maternales und fetales Blutflußprofil während der Geburt, published in the same issue).

The health status of the fetus depends mainly on the oxygen supply to the fetal brain. The fetal heart rate patterns however, correlate only poorly with the fetal oxygen supply. For decades there has been a need in obstetrics for a reliable, easy-to-use method for the everyday routine of continuously measuring the fetal oxygen supply.
The continuous monitoring of the oxygen partial pressure was not successful (Huch 1972, 1973; Aarnoudse 1985). The oxygen partial pressure of the fetal scalp provides very restricted information only about the oxygen supply to the brain.
The most important parameter physicians have access to outside the brain is oxygen saturation, since it directly reflects the oxygen transport capacity, if the hemoglobin concentration is known. The pulse oximetry (Nakajima 1975) is able to focus on the oxygen saturation of the hemoglobin fraction in arterial blood relative to the total hemoglobin. According to the Lambert-Beer law light is absorbed on the way through tissue.

Back in 1989 the scientific community could not imagine that pulse oximetry would ever play an important role in obstetrics.
In principle there are two pulse oximetry methods: for pulse oximetry it is necessary to transilluminate a portion of tissue. This can be done either according to the reflection principle or according to the transmission principle. In reflex pulse oximetry light emitters and light receivers are positioned next to each other, accordingly reflections at both superficial and lower tissue levels play the dominant role (along with transmission, absorption and scatter). In transmission pulse oximetry light emitters and receivers are positioned on opposing sides of the tissue, accordingly transmission through the respective tissue volume plays the dominant role (along with absorption and scatter). In "born humans", either newborn or adult, the transmission principle has gained acceptance since it avoids a severe error source of reflection pulse oximetry, i.e. the light shunt in the superficial skin layers: there is no light traveling through superficial tissue layers not carrying the relevant biological information. Usually, in transmission pulse oximetry a finger, a toe or an earlobe is transilluminated. For fetal use, however, there have been until now only probes which work according to the reflection principle, for reasons easy to understand (Huch, et al., Butterwegge, Gardosi). Even though fetal reflection pulse oximetry devices for fetal monitoring are offered worldwide, this type of fetal monitoring has not succeeded due to its lack of accuracy and reliability. At the conference of the DGGG in June 2000 one of the main users (Schmidt) explicitly warned against relying on the results of these devices.
Only the pure transmission of tissue with light - which means the exclusion of any shunt light - allows to correctly conclude the arterial oxygen saturation.
The exclusion of shunt light is an important but often inexcusably ignored prerequisite of pulse oximetry. In reflex pulse oximetry there are substantial and unavoidable fractions of shunt light so that the reflex pulse oximetry contains serious errors. For this reason it is transmission pulse oximetry which has been so extremely successful in the last two decades in hospitals and ambulances. To the expert this is hardly surprising.
In the fetus, in attempting to achieve a transmission of tissue with light, there are no natural sites for application - neither a finger nor an earlobe can be reached. Accordingly several research groups have been tempted to get involved in reflex pulse oximetry (Gardosi, Huch, Butterwegge). These have most probably chosen their areas of research with an eye on potential commercial exploitation. Transmission pulse oximetry, however, has no longer been available due to the early patents of Buschmann. So it turned out that Buschmann was the first and due to the patents the only researcher to undertake the attempt to make the extremely successful transmission pulse oximetry available as a fetal monitoring sub partu.
The only principle that remained for the other research groups was the reflection principle and the hope that devices based on this principle would work. However, reflection pulse oximetry suffers from inevitable severe measurement errors which can easily be deduced from pulse oximetry theory. Thus, the inaccuracy of reflection pulse oximetry is a basic problem and can neither be overcome by nice device design nor by an aggressive marketing. As expected, these reflection pulse oximetry devices have not been convincing in hospital.

Buschmann (Lancet 1992) developed a fetal scalp electrode (FSE) which works according to the transmission principle. Since the fetus does not provide any sites which can naturally be transilluminated, transmission pulse oximetry can only be realized with invasive sensors: The transmission of the tissue has to take place either from inside to outside or vice versa or both, light emitter and light receiver are positioned inside the tissue. The scalp electrode turns out to be the ideal sensor de­sign for Fetal Transmission Pulse Oximetry.

• It has been well recognized for decades in obstetrics and has been well established.
• It is invasive and can thus house the optical components.
• The fixation to the fetal tissue is reliable and reproducible.

Since the conditions of the oxygen transport in the fetus are entirely different from those in the adult, the oxygen saturation of the fetus normally ranges between 50 and 60 %, but it can also drop to values below 10 %. Pulse oximeters designed for adults or newborns are unsuitable for measurements of the fetus (Gary et al 1969). Accordingly the probes as well as the pulse oximetry devices, the respective software and the calibration had to be specially developed for the fetal pulse oximetry.
The transmission pulse oximetry which the concept presented here is based on and which has proved to be successful worldwide and million fold in adults and newborns has now shown excellent results in first clinical tests on the fetus as well. Transmission pulse oximetry has shown an accuracy and a sensitivity which exceeds all expectations. Without overdoing it, this new fetal monitoring can be called a sensational new device: Even though the clinical studies have only just started, the following very interesting phenomenon could be proven: DIPs of class 2 are associated with a DIP-synchronous drop in oxygen saturation - this drop reaching oxygen saturation values as low as 10 %. These not yet published data are outstanding worldwide.
It can be assumed that the Fetal Transmission Pulse Oximetry for obstetrics will become a revolution similar to the one when adult transmission pulse oximetry was introduced back in the 80's, with comparable chances for a company active in the biomedical field.

In future you will find here single plots of fetal oxygen saturation as measured with the BLM-system (sensor FOTOS, software, hardware) to demonstrate the power of the new technology

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