B17. Pregnancy induced hypertension and preeclampsia

Page created on December 29, 2021. Last updated on February 18, 2022 at 13:42

Hypertensive disorders of pregnancy

Definition and epidemiology

Hypertensive disorders of pregnancy are disorders characterised by hypertension in pregnancy, more specifically the second half of pregnancy. The most important are preeclampsia and eclampsia, which may cause severe morbidity and mortality for both the mother and foetus, and so screening, prevention, and treatment of these disorders is important. These disorders can progress to become serious and life-threatening over hours or days. In most cases they resolve within hours or days after delivery.

There are four major hypertensive disorders of pregnancy:

  • Chronic hypertension
  • Gestational hypertension
  • Preeclampsia/eclampsia
  • Preeclampsia superimposed on chronic hypertension

Hypertensive disorders of pregnancy affect 5 – 10% of pregnant women. Gestational hypertension and preeclampsia are the most common forms.

The department of Obstetrics and Gynaecology at POTE does research on pre-eclampsia, especially prof. Péter Tamás and dr. Eszter Hantosi. It might be useful to know some of this research on the exam, so I’ll include a bit about it.

Types

Hypertension is defined as SBP > 140 mmHg or DBP > 90 mmHg.

Chronic (pre-existing) hypertension refers to the case where the pregnant woman was already diagnosed with hypertension before pregnancy or was diagnosed during pregnancy but before 20 weeks of gestation. 20% of these cases go on to develop superimposed preeclampsia.

Gestational hypertension refers to the case where the pregnant woman develops hypertension after 20 weeks of gestation, after having been previously normotensive. 25% of these cases go on to develop preeclampsia.

Preeclampsia refers to the case where gestational hypertension is present AND either of the following are present:

  • Proteinuria (> 0,3 g/day)
  • Proteinuria (> 5 g/day)
  • Severe hypertension (> 160/110 mmHg) despite antihypertensive treatment
  • Thrombocytopaenia
  • Renal insufficiency
  • Impaired liver function
  • Pulmonary oedema
  • Persistent cerebral or visual symptoms (headache, irritability, visual disturbance)

If any of the bolded findings are present, the condition is known as preeclampsia with severe features.

We can distinguish two subsets of preeclampsia. Early-onset preeclampsia occurs before week 34 and is associated with abnormal foetal development and worse outcomes. Late-onset preeclampsia occurs later does not cause abnormal foetal development and has a better prognosis. Late-onset preeclampsia accounts for 90% of cases.

The two types of preeclampsia are characterised by different haemodynamic changes. Early-onset preeclampsia is characterised by low cardiac output, reduced intravascular volume, and high vascular resistance, while late-onset preeclampsia is characterised by high cardiac output, increased intravascular volume, and normal or low vascular resistance. As such, some researchers (including those at the department) are of the opinion that preeclampsia should not be classified according to time of onset but rather to the haemodynamic phenotype, as hypoperfusion type and hyperperfusion type, instead.

Eclampsia refers to the case when a patient with preeclampsia develops generalised tonic-clonic seizures during pregnancy, delivery, or the first 7 days after delivery. Seizures are sometimes followed by coma.

Preeclampsia superimposed on chronic hypertension refers to the case when a patient with chronic hypertension develops a sudden increase in blood pressure or new onset of a feature of preeclampsia, like proteinuria.

HELLP syndrome is associated with preeclampsia, especially preeclampsia with severe features. It is covered in topic A15.

Etiology

The cause of hypertensive disorders of pregnancy is unknown. However, some risk factors are known:

  • Pregestational
    • Previous preeclampsia, or family history
    • Nulliparity
    • Obesity
    • Diabetes mellitus
  • Gestational
    • Gestational diabetes

Most cases occur in the woman’s first pregnancy.

Pathomechanism

The pathomechanism of these disorders are not well known. A dysfunction of the placenta is present, but maternal factors are also important.

Insufficient remodelling of the spiral arteries of the decidua may contribute to early-onset preeclampsia by causing placental hypoperfusion. Late-onset preeclampsia is likely rather due to excessive salt and water retention.

Maternal symptoms and organ injuries are caused by systemic inflammation with endothelial dysfunction due to release of proinflammatory mediators from the dysfunctional placenta. Hypertension occurs due to vasoconstriction, and organ dysfunction occurs due to microthrombosis.

It’s also not well known how eclampsia causes seizures. However, a loss of cerebral autoregulation is probably involved.

Clinical features

Chronic and gestational hypertension are asymptomatic. Preeclampsia may be, or it may cause symptoms like headache, generalised oedema, visual disturbances, dyspnoea, epigastric pain, etc. Facial oedema can cause a characteristic facial puffiness.

Almost all who develop eclampsia have warning symptoms like severe headache or other severe symptoms of preeclampsia before the seizures, as well as a known diagnosis of preeclampsia.

Diagnosis and evaluation

Diagnosis is made based on blood pressure measurement and organ function tests, including:

  • Urinalysis (especially for proteinuria)
  • Thrombocytes
  • Liver function tests
  • Kidney function tests

NST and ultrasound should also be performed to monitor the foetal health. Doppler examination of the umbilical artery (for IUGR) is important. Presence of a bilateral notch on the flow profile of the uterine artery is associated with preeclampsia.

Treatment

Patients with preeclampsia are usually admitted and are monitored and treated inpatient.

Antihypertensive treatment is indicated in case of severe hypertension (> 160/110 mmHg) to decrease the risk for maternal stroke. Labetalol, nifedipine, and methyldopa are safe in pregnancy and may be used. However, antihypertensive treatment does not treat the underlying problem and does not improve the prognosis of the condition, and so is not routinely indicated.

Magnesium sulphate (MgSO4) decreases the risk for eclampsia and is indicated in case of worsening or serious preeclampsia. It also treats the seizures and is therefore indicated ASAP in case of manifest eclampsia.

The only definitive treatment for preeclampsia and eclampsia is delivery. An important part of the management of these disorders is therefore to evaluate the risk/reward of inducing delivery versus waiting (expectant management), considering the risks for both the mother and foetus. In case of earlier gestational weeks, waiting may increase the risk for the foetus to survive birth. In case of later gestational weeks (> 37), delivery is induced.

The department at POTE is researching the use of furosemide in late-onset preeclampsia, based on the theoretical background that patients with late-onset disease may have increased intravascular volume. They also state that the other antihypertensives are counterintuitive to use because they’re vasodilators and the vascular tone is often already low.

Prevention

Acetylsalicylic acid (75 mg/day taken at night from week 12 until birth) decreases the risk for preeclampsia in those at high risk. “High risk” includes previous preeclampsia, chronic kidney disease, diabetes, etc.

Complications

  • Maternal
    • Haemorrhagic stroke
    • HELLP syndrome
    • Pulmonary oedema
    • Renal insufficiency
    • Placental abruption
    • DIC
  • Foetal
    • Intrauterine growth restriction (in early-onset type)
    • Increased birth weight (in late-onset type)
    • Perinatal asphyxia
    • Prematurity
    • Intrauterine demise

Prognosis

In almost all cases, the conditions resolve within hours or days after delivery. However, women who’ve developed gestational hypertension or preeclampsia are at higher risk of cardiovascular disease, as well as repeat hypertensive disorders in later pregnancies.

Leave a Reply

Inputting your name is optional. All comments are anonymous.