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Hypertension in Pregnancy

Background

The category “Hypertensive Diseases of Pregnancy” remains the leading cause of direct maternal deaths in South Africa (Saving Mothers – Confidential Enquiries into Maternal Deaths 1999-2001; Department of Health, Pretoria).

Pre-eclampsia, a multiorgan disease unique to pregnancy, clinically evident by the presence of hypertension and proteinuria, in its severe forms is the commonest cause of maternal and perinatal mortality and morbidity due to hypertensive diseases of pregnancy.

Prevention of Pre-eclampsia Initial screening, identification and referral of patients for specialist input is essential. Screening must be done at primary health care facilities. The following is essential to check:- blood pressure, proteinuria, excessive weight, oedema and clinical signs of IUGR at each visit. Women at risk of pre-eclampsia First pregnancy Previous pre-eclampsia Age ≥40 years Body Mass Index ≥35 Family history of pre-eclampsia Booking diastolic BP ≥80 mm Hg Multiple pregnancy Medical conditions pre-existing hypertension pre-existing renal disease pre-existing diabetes presence of antiphospholipid syndromeOnce identified refer for specialist input. Definitions of terms used in this guideline Hypertensiondiastolic blood pressure of ≥90 mm Hg systolic blood pressure of ≥140 mm HgNew hypertension – Hypertension ≥20 weeks of gestation in women who had a diastolic blood pressure of <90 mm diastolic before 20 weeks pre-existing hypertension – diastolic blood pressure of ≥90 mm hg before pregnancy or at booking prior to 20 weeks gestation new proteinuria – presence of proteinuria as shown by ≥300 mg />ℓ on dipstick testing, a protein to creatinine ratio of ≥30 mg/mmol on a random sample, or a urine protein excretion of ≥300 mg in 24 hours. Quantified Proteinuria – urine protein excretion ≥300 mg in 24 hours. Pre-eclampsia – new hypertension and quantified proteinuria after 20 weeks gestation, confirmed if it resolves following delivery. How should the blood pressure be taken in pregnancy? The woman should be rested and sitting at a 45o angle. The blood pressure cuff should be of appropriate size and placed at the level of the heart. A minimum of 2 readings over a period of time should be used to confirm the diagnosis. Korotkoff phase 5 is the appropriate measurement of diastolic blood pressure in pregnancy. Automated blood pressure readings should be used with caution as they may be inaccurate in pre-eclampsia. How do we measure proteinuria? Proteinuria is usually detected by visual urinary dipstick measurement and a value of at least 2+ is regarded as significant. Twenty-four hour quantitative urinary protein measurements are usually recommended because of the high rate of false positives associated with the visual dipstick method. The severity of pre-eclampsia is based on the level of high blood pressure and quantity of proteinuria.

The following are indications of severe disease:- Eclampsia – convulsions associated with high blood pressure and proteinuria Severe hypertension: systolic blood pressure over 170 mm Hg or diastolic blood pressure over 110 mm Hg (3 blood pressure readings in 15 minutes) with at least a proteinuria of 1+ or 1 g on semiquantitative testing. Moderate hypertension – systolic hypertension over 140 mm Hg or diastolic hypertension over 90 mm Hg with at least ++ proteinuria or 3 g on semiquantitative testing and any of the following symptoms: headache, visual disturbances, epigastric pain, signs of clonus, papilloedema, liver tenderness, platelet count <100 x 109 />ℓ, liver enzymes (ALT >50 iu/ℓ). How should we control very high blood pressure? Antihypertensive treatment should be used when the blood pressure is ≥160 mm Hg systolic or ≥110 mm Hg diastolic. In the presence of other markers of potentially severe disease e.g. thrombocytopenia, oliguria and or abnormal liver function tests, treatment should be started at lower degrees of hypertension. Avoid atenolol, ACE inhibitors and diuretics. Use antihypertensives you are familiar with. Commonly used antihypertensives in pregnancy are Methyl Dopa 500 mgms 6 hourly, Nifedipine orally, 10 mgms 6 hourly or Nifedipine XL 30 mg daily, Apresolene 25-50 mgms tid. Labetalol orally is commonly used in the United Kingdom. Antihypertensive agents can prolong pregnancy allowing the fetus to grow to a viable stage, while minimizing complications in the woman. Therefore in patients with mild or moderate hypertension, methyl dopa or Adalat XL are the antihypertensives of choice. All women with a diagnosis of hypertensive disorders of pregnancy, should be admitted for initial assessment of the mother and fetus, and appropriate blood and imaging investigations.

Note well: In the presence of severe hypertension and a viable baby, treatment should be haemodynamic stabilization and delivery of the baby. Hypertensive emergencies in pregnancy (impending eclampsia, eclampsia) Use Magnesium Sulphate to prevent convulsions. The usual regimen is 6G IVI slowly over 15-20 minutes then 1 G/hour via an infusion pump. Magnesium Sulphate should be used for at least 24 hours. Lower very high blood pressures with either an infusion of labetalol, 5 mg/ml at a rate of 4 ml/hour via a syringe pump. The infusion rate should be doubled every ½ hour to a maximum of 32 ml (160 mg) / hour until the diastolic blood pressure has fallen and stabilized at an acceptable level (95-100 mm Hg diastolic) Labetalol can also be used as an intermittent bolus infusion – 50 mg (= 10 ml of labetalol 5 mg/ml) given over at least 1 minute. This should have an effect by 5 minutes and should be repeated until the diastolic blood pressure is lowered to between 95-100 mm Hg. Labetalol bolus infusions can be repeated to a maximum dose of 200 mg. The pulse rate should remain over 60 beats/minute. An alternate choice is Nifedipine – 10 mg oral tablet (not a slow release tablet). Nifedipine should not be given sublingually, should not be chewed or bitten or used buccally. Antenatal Fluid Management Careful fluid balance is aimed at avoiding fluid overload. Pre-eclamptics are prone to pulmonary oedema. In the patient with oliguria, a central venous line is recommended. Delivery – remember to achieve haemodynamic stabilization initially and plan delivery for the best time and the best day. Post Delivery Observations – remember to observe patients with severe hypertension for at least 24 hours following delivery in a high dependency area. Post delivery a step-down approach should be taken to reducing antihypertensive drugs, rather than an abrupt cessation. Methyl Dopa should be changed to an ACE inhibitor if appropriate. all women with hypertensive states in pregnancy should return 1 and 6 weeks following delivery. If hypertension or proteinuria persists, further investigations to elucidate the underlying causes must be performed.NB Guidelines for fetal monitoring are not provided but remember to be aware of abruptio placentae and intra-uterine growth restriction.

FRANCO GUIDOZZI 2007