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Pre-eclampsia is said to be present when hypertension arises in pregnancy (pregnancy-induced hypertension) in association with significant protein in the urine. (Note: in the U.S. the word is spelled without the hyphen "preeclampsia" and in most parts of the rest of the world with a hyphen "pre-eclampsia".) It should not, however, be considered primarily as a blood pressure disorder: such a simplistic view detracts from the fundamental pathological process underlying this condition. It is a multi-system disorder which occurs only in pregnancy and which can affect every organ system in the body, particularly the liver, lungs, kidney, brain and cardiovascular system. It appears to be caused by some placental factor, the exact nature of which is unclear, and the pathophysiology involves endothelial dysfunction. Pre-eclampsia is unpredictable in onset and progression and for the majority of cases presenting pre-term. It is incurable except by ending the pregnancy. It may also present up to 6 weeks post-partum. It is the most common dangerous complication of pregnancy--impacting both the mother and the fetus. It is a very heterogeneous condition such that in some instances the most prominent feature may be liver damage, in others it may be kidney dysfunction and in still others it may be, as the name suggests, the blood pressure itself.
Diagnosis Pre-eclampsia is diagnosed when a pregnant woman develops high blood pressure (two separate readings taken at least 6 hours apart of 140/90 or more) and 300 mg of protein in a 24 hour urine sample (proteinuria). Swelling or oedema (especially in the hands and face) was originally considered an important sign for a diagnosis of pre-eclampsia, but in current medical practice only hypertension and proteinuria are necessary for a diagnosis. It is important to note, however, that unusual swelling, particularly of the hands, feet or face, notable by leaving an indentation when pressed on, can be significant and should be reported to your provider. Some women develop high blood pressure without the proteinuria (protein in urine); this is called Pregnancy-induced hypertension (PIH) or gestational hypertension. Both pre-eclampsia and PIH are regarded as very serious conditions and require careful monitoring of mother and baby. Appearance Pre-eclampsia is much more common in the first pregnancy (5-7% of births) and usually becomes evident in the third trimester (and virtually always after the 20th week of pregnancy). It is also more common in women who have preexisting hypertension, diabetes, autoimmune diseases like lupus, various inherited thrombophilias like Factor V Leiden, or renal disease, in women with a family history of pre-eclampsia, and in women with a multiple gestation (twins, triplets and more). The single most significant risk for developing pre-eclampsia is having had pre-eclampsia in a prior pregnancy. Pre-eclampsia may also occur in the immediate post-partum period or up to 6-8 weeks post-partum. This is referred to as "postpartum pre-eclampsia". The most dangerous time for the mother is the 24-48 hours postpartum and careful attention should be paid to pre-eclampsia signs and symptoms. Causes Pre-eclampsia is thought to be caused by a shallowly implanted placenta which becomes hypoxic, leading to upregulated inflammatory mediators secreted by the placenta and acting on the vascular endothelium. If severe, it progresses to fulminant pre-eclampsia, with headaches, visual disturbances, and epigastric pain, and further to HELLP syndrome and eclampsia. Placental abruption is associated with hypertensive pregnancies. These are life-threatening conditions for both the developing fetus and the mother. Pathogenesis Despite extensive research, the exact aetiology and pathophysiology of the condition remain unclear. It is likely, however, that inadequate placental perfusion resulting from inadequate placental invasion precipitates the release of some form of chemical trigger which, in susceptible mothers, leads to endothelial damage, metabolic changes and a form of inflammatory response. Studies suggest that hypoxia resulting from inadequate perfusion upregulates sFlt-1, a VEGF and PlGF antagonist, leading to a damaged maternal endothelium and restriction of placental growth.• In addition, endoglin, a TGF-beta antagonist, is elevated in pregnant women who develop preeclampsia. • Soluble endoglin is likely upregulated by the placenta in response to an upregulation of cell-surface endoglin produced by the maternal immune system, although there is also the potential that sEng is produced by the maternal endothelium. Levels of both sFlt-1 and sEng increase as severity of disease increases, with levels of sEng surpassing levels of sFlt-1 in HELLP syndrome cases. It is important to note that both sFlt-1 and sEng are upregluated in all pregnant women to some extent, supporting the idea that hypertensive disease in pregnancy is a normal pregnancy adaptation gone awry. As natural killer cells are intimately involved in placentation and as placentation involves a degree of maternal tolerance for a foreign placenta which requires maternal resources for its support, it is not surprising that the maternal immune system might respond more negatively to the arrival of placentae under certain circumstances, such as a placenta which is more invasive than normal. Initial maternal rejection of the placental cytotrophoblasts may be the cause of the inadequately remodeled spiral arteries in those cases of preeclampsia associated with shallow implantation, leading to downstream hypoxia and the appearance of maternal symptoms in response to upregulated sFlt-1 and sEng. (See parent-offspring conflict.) It has been documented that fetal cells such as fetal erythroblasts as well as cell-free fetal DNA are increased in the maternal circulation in women who develop preeclampsia. These findings have given rise to the hypothesis that preeclampsia is a disease process by which a placental lesion such as hypoxia allows increased fetal material into maternal circulation that leads to an inflammatory response and endothelial damage ultimately resulting in preeclampsia and eclampsia..• Placental invasion In normal pregnancy trophoblastic invasion of the maternal spiral arteries causes the diameter of these arteries to increase around five-fold, converting the supply from a high resistance low flow system to one with a low resistance and high flow. In pre-eclampsia adequate invasion does not seem to occur, or is limited to the decidual portions of the vessels, and the result is inadequate placental blood flow. Inadequate placental invasion is also associated with fetal growth restriction, but not all those with this form of growth restriction develop pre-eclampsia. As the degree of trophoblastic invasion is regulated by the maternal decidual barrier, probably by the action of a specific form of leucocyte, it has been suggested that the primary aetiological factor in pre-eclampsia may be immunological in origin. The predominance of pre-eclampsia in first pregnancies, and the protective effect of parity, further supports an immunological mechanism but the exact nature of this has yet to be elucidated. Nonetheless inadequate placental invasion certainly occurs and may be the trigger to release some factor, or alter the level of some factor, which brings about a response in a susceptible mother. Currently sFlt-1 upregulated in response to placental hypoxia and sEng upregulated in response to cell-surface Eng in conjunction are considered the most likely candidates. Maternal susceptibility As noted above, placentally mediated growth restriction can occur in isolation, but is also common with pre-eclampsia. It is therefore reasonable to assume that, while inadequate invasion occurs in both, only mothers who develop pre-eclampsia have a susceptibility to the placental stimulus. This susceptibility may be genotypic or phenotypic. The evidence for genotypic susceptibility is strong. It has long been recognised that there is a familial pattern to pre-eclampsia and studies of pregnant women who have developed eclamptic seizures show that these women are more likely to have had sisters, mothers or grandmothers who have suffered from the same problem. Analysis suggests a single gene inheritance, either recessive with high penetrance, or dominant with incomplete penetrance. A number of genes on a variety of chromosomes have been found to be associated with pre-eclampsia, as has an angiotensin gene variant on chromosome 4. A genetic pre-disposition is also observed in those with certain congenital thrombophilias. Certain phenotypes are also more susceptible. Those with insulin resistance and central obesity are at increased risk of pre-eclampsia, possibly on account of an exaggerated metabolic response. Those with systemic lupus erythematosus are also at increased risk, possibly because of an exaggerated immune response, and it has already been noted that those with a congenital thrombophilia are more likely to develop problems, possibly because of an increased coagulation response. These associations suggest that the pathophysiology involves a significant inter-relation between metabolic processes, an immunological response and coagulation problems, possibly mediated through endothelial damage. These maternal responses are now considered. Metabolic changes, inflammatory response and endothelial damage In normal pregnancy there is increased biosynthesis of eicosanoids – particularly prostacyclin (PGI2), a vasodilator with platelet inhibitory properties, and thromboxane A2, a vasoconstrictor with a tendency to stimulate platelet aggregation. As both usually increase in proportion to each other, there is a net neutralization and homeostasis is maintained. This homeostasis is disrupted in pre-eclampsia because of a relative deficiency in prostacyclin due either to a decrease in its synthesis and/or an increase in the production of thromboxane A2. This imbalance leads to vasoconstriction, hypertension, and platelet stimulation. These observations form the theoretical basis behind the use of low-dose aspirin, a prostaglandin inhibitor, in preventing pre-eclampsia. The dose of aspirin required to inhibit thromboxane synthesis is less than that required for prostacyclin inhibition and it should, in theory, therefore reduce the vascular and thrombotic effects. Normal pregnancy is also associated with an increase in angiotensin II, a potent vasoconstrictor, yet despite this it is usual in pregnancy for the peripheral vascular resistance to fall. This appears to be because of a resistance to effects of angiotensin II in normal pregnancy, a phenomenon which seems to be lost in women who are destined to develop pregnancy-induced hypertension. This suggests that abnormalities in the renin-angiotensin-aldosterone system may play a role in the pathogenesis of the condition. Most agree that it seems unlikely, however, that derangements in this system are the primary cause of the pre-eclampsia. In addition to these changes, there also appears to be some form of inflammatory process. There is an increase in the pro-inflammatory cytokines, evidence of neutrophil activation, and an increase in substances capable of causing inflammatory damage, particularly proteases and oxygen radicals. These are also recognised to damage vessel walls. Other systemic metabolic changes include hypertriglyceridaemia and a significant increase in free fatty acids, both associated with acute atherosis. Some of these metabolic changes may cause endothelial damage, which in turn promotes platelet adhesion, stimulates clotting activity and disturbs the normal physiological modulation of vascular tone, further amplifying the response. The resulting secondary damage to other organs gives rise to the clinical features of gestational hypertension, pre-eclampsia, eclampsia and the HELLP syndrome. Therapy The only known treatment for eclampsia or advancing preeclampsia is delivery, either by induction or Caesarean section. However, post-partum pre-eclampsia may occur up to 6 weeks following delivery even if symptoms were not present during the pregnancy. Post-partum pre-eclampsia is dangerous to the health of the mother since she may ignore or dismiss symptoms as simple post-delivery headaches and edema. Hypertension can sometimes be controlled with anti-hypertensive medication, but any effect this might have on the progress of the underlying disease is unknown. In some cases women with preeclampsia or eclampsia can be stabilized temporarily with magnesium sulfate intravenously to forestall seizures while steroid injections are administered to promote fetal lung maturation. When induced delivery needs to take place before 37 weeks gestation, it is accepted that there are additional risks to the baby from premature birth that will require additional monitoring and care. Studies into supplementation with antioxidant vitamins C and E found no change in preeclampsia rates.• Calcium supplementation in women with low-calcium diets found no change in preeclampsia rates but did find a decrease in the rate of severe preeclamptic complications.• Aspirin supplementation is still being evaluated as to dosage, timing, and population and may provide a slight preventative benefit in some women, however significant research has been done on aspirin and the results thus far are unimpressive.• There is insufficient evidence to recommend either exercise• or bedrest• as treatments. Studies of protein/calorie supplementation have found no effect on preeclampsia rates, and dietary protein restriction does not appear to increase preeclampsia rates.• As of 2006, Pfizer's Viagra (sildenafil citrate) was in Phase II clinical trials for the treatment of pre-eclampsia. See also Reference Footnotes | ||||||||
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