Hypertension in pregnancy

Why is hypertension a problem in pregnancy?

Hypertensive disorders in pregnancy are a major cause of maternal, fetal and neonatal morbidity and mortality, both in developing and developed countries. Hypertension is the most common medical problem in pregnancy, complicating up to 15% of pregnancies and accounting for about a quarter of all antenatal admissions in the UK.

Women with hypertension in pregnancy have a higher risk of complications such as:

• Abruptio placentae.

• Cerebrovascular accident.

• Disseminated intravascular coagulation.

The fetus has an increased risk of:

• Intrauterine growth restriction.

• Prematurity.

• Intrauterine death.

Hypertension in pregnancy includes:

• Gestational hypertension - pregnancy-induced hypertension which develops after 20 weeks of gestation and may be either transient hypertension of pregnancy or chronic hypertension not identified until the latter half of pregnancy. This might progress to become:
  

  • Pre-eclampsia: pregnancy-induced hypertension plus proteinuria and/or oedema or both.

  • Eclampsia - occurrence of one or more convulsions superimposed on pre-eclampsia. See the separate Pre-eclampsia and eclampsia article.

• Pre-existing hypertension - is defined as a systolic blood pressure (BP) of 140 mm Hg or greater, and/or a diastolic BP of 90 mm Hg or more, either pre-pregnancy or at booking (before 20 weeks). This can exist alone or may develop into:

  • Pre-eclampsia in addition to pre-existing chronic hypertension.

Blood pressure (BP) measurement¹

• Use a sitting or semi-reclining position so that the arm to be used is at the level of the heart.

• Do not take the BP in the upper arm with the woman on her side, as this will give falsely lower readings.

• Korotkoff phase 5 measurements should be used for taking the diastolic pressure, except on those rare instances when sounds continue to be heard to 0 mm Hg when Korotkoff phase 4 can be used.²

Diagnosing those who are at risk of pre-eclampsia

Placental growth factor (PLGF)-based blood tests have now been recommended by the National Institute for Health and Care Excellence to help decide on care for those with suspected preterm pre-eclampsia (between 20 and 36⁶ weeks of pregnancy).³ They will help rule in, or rule out pre-eclampsia.

There are four tests recommended but each has different instructions on timing of use and, therefore, should be used according to its indications. These tests are:

• DELFIA Xpress PLGF 1‑2‑3.

• DELFIA Xpress sFlt‑1/PLGF 1‑2‑3 ratio.

• Elecsys immunoassay sFlt‑1/PLGF ratio.

• Triage PLGF Test.

PLGF-based testing may particularly benefit groups at higher risk of severe adverse pregnancy outcomes, such as people from African, Caribbean and Asian family backgrounds.

These tests are recommended to help plan safe-care and a safe birth for those with pre-eclampsia. They can also help to identify people unlikely to develop pre-eclampsia, and therefore reduce unnecessary hospitalisation. They will be used once in a pregnancy when a person presents with an episode of symptoms indicating a possibility of preterm pre-eclampsia. They are not recommended in anyone with multiple birth (twins or more) and cannot be used for repeat testing within one pregnancy, due to a lack of evidence.

Of note, BRAHMS sFlt‑1 Kryptor/BRAHMS PLGF plus Kryptor PE ratio is not recommended.

Management of hypertension in pregnancy

Management depends on the woman's BP, gestational age and blood flow in the placenta. Non-pharmacological management is recommended for many women but is not recommended when there is the presence of associated maternal and fetal risk factors. Non-pharmacological management includes close supervision, limitation of activities, and some bed rest in the left lateral position.¹

Patients with pre-existing hypertension who become pregnant

• Review medication and inform the patient of the risks involved with some medications. Those on angiotensin-converting enzyme (ACE) inhibitors or angiotensin-II receptor antagonists (AIIRAs) should be switched from these as soon as possible, as there is an increased risk of congenital abnormalities if these drugs are taken during pregnancy. Ideally this will have been done at a pre-pregnancy counselling session; however, if not, it should be done as early as possible in the pregnancy. Diuretics should be avoided, as they can reduce the blood flow in the placenta.

• Aim to keep BP lower than 150/100 mm Hg (140/90 mm Hg if there is target organ damage) although do not seek to lower the diastolic level below 80 mm Hg.

• Test for proteinuria regularly - if this shows ≥1+ arrange a spot urinary protein:creatinine ratio to quantify proteinuria.⁴ There is significant proteinuria if urinary protein:creatinine ratio is >30 mg/mmol (treat the patient as for pre-eclampsia) - see the separate Pre-eclampsia and eclampsia article.

• Ultrasound examination is used to assess fetal growth and amniotic fluid volume (with umbilical artery Doppler velocimetry) at 28-30 weeks and 32-34 weeks.

• After delivery - If methyldopa is used - switch back to the pre-pregnancy antihypertensive regime within two days of delivery.

Offer placental growth factor (PlGF)-based testing to help rule out pre-eclampsia between 20 weeks and up to 35 weeks of pregnancy, if women with chronic hypertension are suspected of developing pre-eclampsia - see above.⁴

Gestational hypertension

• Assess severity:
  

  • Mild: 140-149/90-99 mm Hg. For patients presenting before 32 weeks (or at high risk of pre-eclampsia), measure BP twice a week; otherwise, measure BP no more often than weekly. Check urine for protein at each visit.

  • Moderate: 150-159/100-109 mm Hg. Monitor BP twice a week - start labetalol (alternatives are methyldopa or nifedipine) to keep systolic BP <150 mm Hg and diastolic BP between 80-100 mm Hg. Dip urine for protein at each visit. Arrange initial blood tests for FBC, electrolytes, renal function and LFTs. Subsequent blood tests are not necessary if there is no proteinuria.

  • Severe: ≥160/110 mm Hg. Admit to hospital and treat as for moderate (above) to keep systolic BP <150 mm Hg and diastolic BP between 80-100 mm Hg. Measure BP at least four times a day and check urine for protein daily. Weekly blood tests for FBC, electrolytes, renal function and LFTs. Check BP and urine twice weekly (and continue weekly blood tests) when discharged (once BP is in the target range).

• Perform ultrasound examination at 34 weeks to assess fetal growth and amniotic fluid volume (with umbilical artery Doppler velocimetry) if mild or moderate gestational hypertension develops before this time. Arrange these tests and cardiotocography urgently whenever severe gestational hypertension is diagnosed.

• After birth, measure BP daily for the first two days after birth, at least once between day three and day five, then as clinically indicated. Continue on antihypertensive medication but reduce or stop if BP is seen to be falling - particularly if it falls below 130/80 mm Hg. Switch women from methyldopa to an alternative within two days of delivery. Women with mild hypertension not requiring treatment during pregnancy should be started on antihypertensive medication postnatally if their BP is ≥150/100 mm Hg.

Pre-eclampsia

See the separate Pre-eclampsia and eclampsia article.

White coat hypertension

The phenomenon of patients having high BP when seen in a clinic by their medical carer but normal BP in their work or home environment, is well recognised and referred to as white coat hypertension (WCH).

Knowing that WCH exists, there will be a subset of pregnant women diagnosed with gestational hypertension, who will actually have WCH but there is no guidance on how to identify these women. See also the Ambulatory blood pressure monitoring (ABPM) article.

• A study of 155 women with high BP diagnosed for the first time during the first half of their pregnancy, found that 50% of them had normal ABPM readings:⁵

  • In this study, WCH was diagnosed when awake average ABPM ≤130/80 mm Hg at or prior to 26 weeks gestation and ≤135/85 if after 26 weeks of gestation.

  • About 50% of these women continued to have WHC throughout their pregnancy, 40% went on to develop gestational hypertension and 8% developed pre-eclampsia, a lower percentage than in the group who had 'true' hypertension. The women with 'true' hypertension were delivered one week earlier and had babies of lower birth weight, although the caesarean section rate, small-for-gestational-age rates and perinatal mortality were the same in both groups.

• ABPM may be useful in determining whether women with high BP early in pregnancy have 'true' hypertension or WCH. If the latter, pregnancy outcomes appear to be good and unnecessary interventions may be avoided.⁶

• However, a 2002 (not updated) Cochrane review did not find any trial evidence to support the use of ABPM in pregnancy.⁷

• It should be noted that not all ambulatory or automatic BP monitors have been validated in pregnancy and they may underestimate BP.²

• It is important when diagnosing high BP in pregnancy to ensure that it is taken several times and in the least stressful environment. Whilst vital not to miss the diagnosis of hypertension in pregnancy, making the diagnosis in error has significant implications for a healthy woman's antenatal care and possibly the timing and mode of delivery.

Outlook for hypertension in pregnancy (Prognosis)

• Hypertensive diseases of pregnancy remain the second leading cause of direct maternal deaths in the UK.

• However, most women with pre-existing mild-to-moderate hypertension (BP less than 160/110 mm Hg) are at low risk of perinatal complications.

• The risk of complications (eg, pre-eclampsia, placental abruption, impaired fetal growth and premature birth) is increased in severe hypertension.

• Gestational hypertension: similar risks to normotensive women; however, 40% of those presenting before 34 weeks of gestation will go on to develop pre-eclampsia.

Women with hypertensive disorders of pregnancy have an overall risk of recurrence in future pregnancies of approximately 1 in 5.⁴

Hypertensive disorders in pregnancy are also an important risk factor for cardiovascular disease in later life. In a 2017 paper looking at the risk of developing hypertension after having had a hypertensive disorder of pregnancy, 14% developed hypertension in the first decade postpartum, compared with 4% of women with normotensive first pregnancies in their 20s.⁸ The corresponding percentages for women with a first pregnancy in their 40s were 32% and 11%, respectively. In the year after delivery, women with a hypertensive disorder of pregnancy had 12-fold to 25-fold higher rates of hypertension compared with women with a normotensive pregnancy.

Rates in women with a hypertensive disorder of pregnancy were threefold to 10-fold higher 1-10 years postpartum and remained twice as high even 20 or more years later. Therefore, lifestyle modifications, regular BP control, and control of metabolic factors are recommended after delivery, to avoid complications in subsequent pregnancies and to reduce maternal cardiovascular risk in the future.

Preventing hypertension in pregnancy

• Low-dose aspirin: see recommendation in high-risk groups as detailed under 'Management', above.

• There is currently limited evidence on low-dose calcium supplementation suggesting a reduction in pre-eclampsia, hypertension and admission to neonatal high care, but this needs to be confirmed by larger, high-quality trials.⁹