Hypertensive complications in pregnancy are increasing in prevalence and often cause significant impairments in maternal and foetal mortality and morbidity. Managing and treating these disorders aims to prevent serious cerebrovascular and cardiovascular effects in the mother without compromising foetal well-being.
In the United States of America alone, hypertension occurs in roughly 6-8% of pregnancies among women ages 20-44. Associated complications of hypertension in pregnancies, including pre-eclampsia, eclampsia, and end-organ damage, are leading causes of maternal and foetal morbidity and mortality worldwide. The main strategy in the treatment of hypertension in pregnancy is to prevent any cerebrovascular and cardiac complications for the mother whilst preserving the uteroplacental and foetal circulation and, limiting medication toxicity to the foetus.
Classification of Hypertension Disorders
These hypertensive pregnancy disorders are diagnosed using a variety of tests including blood pressure monitoring, PIGF (placental growth factor) test and urine tests for proteinuria (increased levels of protein in the urine). Blood pressure readings which are higher than 140/90 mm Hg must also be monitored closely.
– Preeclampsia and Eclampsia
High blood pressure and proteinuria of over 300mg, after 20-week gestation, are both characteristics of these disorders. The difference between eclampsia and preeclampsia is that eclampsia is a convulsive, more life-threatening form of pre-eclampsia, which affects 0.1% of all pregnancies. The disorder is thought to be caused by placental malperfusion resulting from an abnormal modelling of the maternal spiral arteries.
– Gestational Hypertension
This disorder is diagnosed by measuring high blood pressure for the first time from a patient, after 20-week gestation alongside the absence of proteinuria. Gestational hypertension is significantly less dangerous than preeclampsia/eclampsia since the patient has not developed renal impairment, hence the absence of proteinuria.
– Chronic Hypertension
Chronic Hypertension in Pregnancy is defined as blood pressure greater than 140mm Hg systolic and/0r 90 mm Hg diastolic, before pregnancy – however many women seek care for chronic hypertension only after becoming pregnant, before 20 weeks of gestation. This disorder is estimated to be present in approximately 3 – 5% of pregnancy and is increasingly more commonly encountered.
The 2 main risk factors contributing to this increasing prevalence of chronic hypertension include obesity and old age, which are also of increasing prevalence in pregnancy. Although many women with chronic hypertension remain stable during pregnancy and delivery, they are at a greater risk of several pregnancy complications, particularly superimposed preeclampsia, placental abruption, and preterm birth.
– Chronic Hypertension with superimposed preeclampsia
This hypertension disorder is the new onset of proteinuria in the setting of hypertension before 20 weeks of gestation. Although, similar to chronic hypertension, this disorder is categorised separately due to the onset of proteinuria which is drastically increases the patients’ risk of HELLP syndrome (Haemolysis, Elevated Liver Enzymes and Low Platelets – a rare liver and blood clotting disorder that can affect pregnancy women).
Overall, there are four main organ systems which can suffer from possible acute complications of hypertensive pregnancies: Cardiovascular, Renal, Hepatic and the Central Nervous System (CNS). For mild to moderate hypertension in pregnancy, maternal risks are small, although they may be adverse consequences of high blood pressure in foetal cerebrovascular development. In contrast, early-onset and severe preeclampsia have a significant risk of later cardiovascular and renal morbidity and mortality, particularly for the mother.
Managing Hypertensive Pregnancy Disorders
– Non-Pharmacological Approaches
In non-pregnant hypertensive patients, lifestyle changes and interventions, including weight loss and reducing salt intake, are often the course of treatment. However, currently, there is no evidence to show that these approaches, such as an exercise and diet programme, is effective in preventing and managing hypertension in pregnancy. A 2010 study concluded that exercise training could reduce preeclamptic features in animal models, both before and after gestation, however human randomised, double-blind trials have not had similar results. Similarly, although obesity is a contributing risk factor for gestational hypertension, no evidence institutes that weight loss interventions could prevent hypertensive disorders in pregnancy.
There are very few non-pharmacological approaches available for managing hypertensive pregnancy disorders, particularly the lack of evidence supporting such approaches. But, bed rest continued to be the most frequent advice for patients with preeclampsia, which has shown to lower blood pressure, promote renal function and, which all will prevent dire complications during delivery. Nevertheless, since the progression of preeclampsia to eclampsia is sudden and without prediction, patients with this condition will be admitted to hospital for observation, where pharmacological approaches are often used due to the severity of the condition.
The only definitive therapy for acute hypertensive syndromes (preeclampsia and eclampsia) is delivery. This is especially when urgent control of blood pressure is necessary, or when the risk of harm to the foetus and/or the mother is significantly high. Delivery must be postponed for as long as possible, to enable foetal maturation, particularly of the respiratory system – Premature babies often have underdeveloped lungs, where not enough surfactant has been produced, which can lead to lung collapse and respiratory distress. The decision for the time of delivery also determines the extent of preeclampsia and the risk of complications, dictated by the current gestational period, liver and renal function tests, coagulation tests, etc. Although delivery is seen as a definitive treatment, expectant management and close observation is appropriate, particularly for patients before 32 weeks gestation as the foetus will be underdeveloped and risk of mortality is high.
– Pharmacological Approaches
The aim of pharmacological approaches during pregnancy is to prevent progression to severe hypertension and maternal complications, and to improve foetal development by prolonging the pregnancy.
The two main pharmacological agents to treat hypertensive pregnancies include anti-hypertensive agents and beta blockers. Anti-hypertensive agents are a class of drugs that are used to treat hypertension, which can be vasodilators or inhibitors of noradrenaline release. However, these medications should be ceased if diastolic blood pressure falls too low, which can result in maternal ischemia and potentially heart failure: low diastolic BP can restrict foetal blood supply, threatening dangerously low oxygen saturation levels. Anti-hypertensive drugs are successful in reducing blood pressure but must be monitored closely to prevent low diastolic BP and to limit the rate of foetal growth restriction. In comparison, beta blockers medications are most preferred for the treatment of hypertension in pregnancies due to its proven safety and efficacy, and no association to adverse maternal or foetal outcomes.
However, the pharmacological management of hypertension in pregnancies remains controversial and understudied, particularly due to the various and complex factors affecting maternal and foetal wellbeing. Furthermore, increases in diversity and variability across patients’ clinical responses to medications require individualised assessments for dosing.
Hypertensive disorders is a common complication of pregnancy and due to the significant risk of morbidities and mortalities, the main issue with managing these disorders is identifying a balance between the maternal benefits from BP control and the foetal risks caused by intrauterine mediation toxicity and potential growth restriction. The treatment of hypertension may improve the risk profile for the mother and baby, and therefore delay delivery to increase survival rates for the foetus, but it does not cure hypertension, and preeclampsia, nor does it delay the progression to preeclampsia.
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Image 1 – https://www.wrh.ox.ac.uk/images/news/improving-the-prediction-of-preeclampsia/responsive_image?ratio=image&scale=w1140
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