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DEVELOPING THE RIGHT STUFF:
Professor Tony Bunn, Director : Technology Development and Transfer Group, Medical Research Council, PO Box 19070
Tygerberg,7505, South Africa.
An empowering, appropriate, affordable and exportable Fetal Health Device
could save the lives of more than 3000 babies in South Africa alone.
Professor Tony Bunn explains how.
Using a 150-year-old scientific principle, scientists at the Medical Research Council (MRC), and Integrated Sensor Systems at the CSIR, have developed and plan to commercialise a low cost and easy to use antenatal Doppler ultrasound device that they believe could save the lives of more than 3000 babies each year in South Africa alone.
The perinatal mortality rate in rural areas in South Africa is approximately 30/1000 with the ratio of intrauterine to neonatal deaths as high as 2:1. Perinatal mortality is defined as the number of intrauterine deaths after 28 weeks gestation and the number of neonatal deaths within 1 week of birth. Within the last few years flow velocimetry of umbilical arterial waveforms using Doppler ultrasound has established itself as a test that significantly improves neonatal outcome.
This remarkable advance was due to well-designed randomised controlled clinical trials in which the Perinatal Mortality Research Unit of the MRC played a significant role. Their work as well as those of other international research groups, led to the following conclusion from a meta-analysis appearing in the American Journal of Obstetrics and Gynecology (1995) Vol 172:5.
"There is now compelling evidence that women with high-risk pregnancies, including pre-eclampsia and suspected intrauterine growth retardation, should have access to Doppler ultrasonographic study of umbilical artery waveforms".
So what is the Doppler Ultrasound device and how does it work?
In simple terms the fetus is both oxygenated and nourished from the mother's placenta. It achieves this through two umbilical arteries, which emerge through the umbilicus of the fetus carrying de-oxygenated and nutritionally depleted blood to the placenta. Here the fetal blood is re-oxygenated and re-nourished and transported back to the fetus in the umbilical vein, which also passes through the umbilicus. The two umbilical arteries are, in fact, coiled around the umbilical vein. The fetal heart is responsible for pumping this blood through the umbilical arteries and veins and, of course, through the fetus itself in order to promote normal growth.
Poor fetal growth is of great concern in developing countries. From the above it is clear that poor intrauterine growth may be caused by placental insufficiency (i.e. the placenta cannot provide sufficient nutrients or oxygen), fetal abnormality or poor maternal nutrition. It is very important to differentiate between these, as early delivery may be mandatory in the case of severe placental insufficiency but contraindicated in the case of a healthy but small fetus resulting from poor maternal nutrition. Routine ultrasound examinations and frequent fetal heart rate monitoring are not possible in developing countries and even tertiary institutions are not all able to provide this facility for excluding severe placental insufficiency.
As mentioned, Doppler Waveform Analysis (DWA) of umbilical waveforms has, over the past decade, established itself as a prime tool for measuring placental insufficiency. In short, the ultrasonic waves reflected back from blood moving towards the probe increases the frequency of the sound waves while receding blood flow reduces the frequency. These changes in frequency are therefore a measure of blood velocity in the umbilical artery, the waveforms of which are graphically represented on a screen. In general, a continuous waveform ultrasonic probe is positioned on the pregnant mother so as to detect the characteristic beating signals from fetal umbilical arteries; these are then processed to produce Doppler waveforms. In a similar way that ECG signals are able to detect heart abnormalities, so alterations in the Doppler waveforms are able to detect placenta abnormalities.
Why and how should the DWA be utilised?
At present about 10 in 100 third trimester pregnancies are clinically diagnosed at antenatal clinics in the Tygerberg region with suspected intrauterine growth retardation and referred to Tygerberg Hospital. These cases are then screened using DWA and about 1 of 10 cases (1 in 100 in total) have growth retardation from placental incompetence and require close monitoring or active intervention to prevent intrauterine death.
Put another way, approximately 9 out of 10 cases of clinically diagnosed fetal growth retardation do not have placental incompetence and are merely normal small fetuses. The monetary cost of referring and evaluating these false positive cases is significant, and the negative psychological impact on the mothers is clearly undesirable.
In the largest survey ever conducted to date the MRC Perinatal Mortality Research Unit has recently shown that the survival rates increased from 48% to 80% in viable fetuses (>28 weeks) with placental incompetence, by active intervention after detection by DWA. Of the approximately 1 million full term pregnancies per year in South Africa there are statistically 10,000 cases with placental incompetence, which would be detected using DWA. Of these 10,000 cases it is estimated that 3,200 would be saved by this detection followed by active intervention.
The MRC unit has also established extremely simple and appropriate guidelines and algorithms for interpretation of the Doppler waveforms. This implies that DWA could become a routine screening tool. Clearly then, the ideal situation would be to place appropriate DWA technology in the hands of registered nurses (midwives) in antenatal clinics and thereby only refer those mothers who have been screened and found to have placental incompetence.
The potential solution:
Though the value of ultrasonographic studies of umbilical arterial waveforms is clearly established, at over R100, 000 per device the cost of using the technology as a routine screening tool in clinics is clearly prohibitive. Building on eight years of research by the Perinatal Mortality Research Unit, as well as local and international scientific advances, a MRC/CSIR consortium are developing a DWA device which will sell for a fraction of the price. In fact, the Department of Arts, Culture, Science and Technology has placed such confidence in the project that it gave the consortium a R1, 5m grant from the Innovation fund in order to achieve this goal.
The DWA design is centred on proven technology, which allows the unit to perform reliably and cost effectively in both first and third world environments. The
ultrasonic Doppler probe connects to an external port of a standard Pentium PC onto which is loaded the developed DWA software. The system allows for a database facility, serial monitoring, plotting of results and "remote access" and "remote control" capabilities will allow for real-time telemedicine to be practiced. The captured data is automatically compared to the onboard proprietary clinical database information and a clinical assessment is suggested to the clinician or midwife.
An evaluation of the DWA against the high cost commercial units is presently underway at the Tygerberg hospital. The resulting data have shown very good correlation between the DWA and other units and the results of this study are to be presented at the International Perinatal Doppler Society Meeting to be held at Spier, Cape town on the 19-21 April 2001.
Although designed with midwives and more equitable health care in mind, the DWA clearly has application to antenatal monitoring at all levels of health care and should prove to be a valuable export commodity.
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