Hypertension/Toxaemia in Relation to Perinatal Hypoxia and Stillbirths

Hypertension/Toxaemia in Relation to Perinatal Hypoxia and Stillbirths

 

Peter von Dadelszen, of The University of British Columbia, Vancouver, Canada began his talk by listing the hypertensive disorders of pregnancy (HDP). There are many classifications and in Figure 5.1 the classifications by three societies (Canadian Hypertension Society (CHS), the National High Blood Pressure Educational Program (NHBPEP) and the Australian Society for the Study of Hypertension (ASSHP)) are listed.

 

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HDP in developing countries is associated with adverse foetal outcome. There is an increased incidence of intrapartum stillbirths and early neonatal deaths with decreases with gestational age. Related to these observations is a report from Dhaka (Figure 5.2) which shows that a high percentage of cerebral palsy follows a pregnancy complicated by eclampsia or pre-eclampsia.

 

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The nature and origin of eclampsia is not clearly understood. What is known is that it is a clinical syndrome almost certainly related to relatively poor placentation, either because of disease within the placenta, or as a placental-foetal mismatch (as with twin pregnancy or foetal macrosomia). Therefore there are many factors which may lead to toxaemia, including, for example, early urinary tract infection.

 

A review of published reports on the association between pre-eclampsia and adverse perinatal outcome is shown in Figure 5.3. The figure compares data from developed and developing countries. (Holland has been listed separately because it uses a different approach to viability from the rest of developed countries.) The data shows that in developing countries there is a much higher rate of stillbirths (IUFD) following pre-eclampsia.

 

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One of the problems of evaluating the perinatal effect of toxaemia is that late toxaemia represents a minimal, if any, threat to the fetus, unlike early toxaemia.

 

Dr. von Dadelszen speculated on the reason that toxaemia is still prevalent since it was first recognized in ancient Egypt. He pointed out the essential features of toxaemia (Figure 5.4) and asked why it still occurs - why it has been “selected”. It may be that, at term, it is adaptive to ensure proper blood flow. Only severe “adaptation” may appear as severe toxaemia or eclampsia.

 

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There is some support for this hypothesis since pre-eclampsia in late pregnancy may be adaptive. For example survival of small for gestational age babies is higher in pregnancies in which the mothers have hypertension. Other examples supporting the hypothesis can be found in Figure 5.5.

 

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Accordingly a trial was undertaken in which hypertension was controlled to determine the effect on foetal outcome. The results (Figure 5.6) showed apparently better outcome when there was no attempt to control blood pressure.  There is also evidence of improved neurodevelopment of infants born of mothers with pre-eclampsia (Figure 5.7).

 

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Dr. von Dadelszen outlined how to avoid adverse perinatal outcomes in the case of pre-eclampsia and other HDP (Figure 5.8).  A test to predict the risk of pre-eclampsia to the fetus and to the mother is needed. PIERS is one predictive test which is used, but a more effective one, especially one which can be employed in low-resource countries, is needed. This would allow high-risk women to be identified and moved to facilities. In turn, this would improve maternal and neonatal outcomes.

 

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A summary of Dr. von Dadelszen’s presentation is shown in Figure 5.9.

 

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