Chapter 13 This chapter is primarily concerned with hypertension in women with child-bearing potential as seen from the point of view of physicians and general practitioners. It is not our remit to cover the obstetrical management of late pregnancy, the delivery of the baby and the immediate puerperium. There is, however, a trend for obstetricians to take an increasing interest in hypertension in women wishing to become pregnant as well as the management of hypertension in early pregnancy. The hypertensive disorders of pregnancy are getting commoner. This is partly due to the trend for women to delay becoming pregnant in order to pursue their careers. The prevalence of pre-pregnancy hypertension (blood pressure of 140/90 mm Hg or more) rises from around 3% in 20-year olds to about 8% in women in their late 30s. The other major cause of the rising prevalence of hypertension in young women is the rising prevalence of obesity and the increasing reliance on convenience foods with their high salt content. The topic of the measurement of bold pressure is covered in detail in Chapter 4. There is an increasing trend to abandon the measurement of blood pressure using a stethoscope. However, if this auscultatory method of measuring pressure is employed, it is important to record the diastolic pressure at the disappearance of the Korotkov sounds (phase 5), not their muffling (phase 4). Most blood pressures are now measured using semi-automatic oscillometric devices. There have been some questions on the accuracy of some of the manometers in pregnancy. Any possible inaccuracy is, however, much less than the inaccuracy caused by hurried, casual, one-off auscultatory measures in a noisy clinic. If the pressure is 140/90 mm Hg or more at the first reading, at least two further readings should be taken, preferably with a semi-automatic device. There is also an increasing interest in 24-h ambulatory blood pressure (ABPM) in pregnancy. Hypertension in pregnancy is the most common cause of maternal death, with a risk of around 10 deaths per million pregnancies in the United Kingdom. Hypertension in pregnancy is also the most common cause of stillbirth and neonatal death. Hypertension occurs in 8–10% of pregnancies and may be the first sign of impending pre-eclampsia – a potentially more serious condition in the second half of pregnancy and in the puerperium. Recent data from the United States show that pregnancy-induced hypertension was the underlying cause in 16% of maternal deaths. More seriously, pre-eclampsia is responsible for one-sixth of all maternal deaths and a doubling of perinatal mortality. Despite accurate figures on the effects of high blood pressure, its precise causes of hypertension in pregnancy are unknown; eclampsia has been referred to as a ‘disease of theories’. In a survey of 6000 women in an unselected obstetric population in Oxford, 0.1% of women had blood pressure ≥160/100 mm Hg before the 20th week of pregnancy. This increased to 3.7% when the maximum antenatal reading at any stage of pregnancy was used. The threshold of ≥140/90 mm Hg was found in 2.0% of women in early pregnancy and 21.5% of women at some stage (usually very near to term). The combined frequency of pre-eclampsia and eclampsia varies between 1 and 6%, depending on parity; the higher figure is seen in first pregnancies. In specialist hypertension obstetric clinics, rates are higher – 11.9 and 16% for women with normal blood pressure and high blood pressure before pregnancy, respectively. Most women with high blood pressure in early pregnancy (before 20 weeks’ gestation) probably have pre-existing or chronic hypertension. This will often be ‘essential’ hypertension, but clinical evaluation is needed, as secondary (usually renal hypertension) may present for the first time in pregnancy. Most women with high blood pressure in late pregnancy have pregnancy-induced hypertension or pre-eclampsia, which complicate chronic underlying hypertension. Unfortunately, many, usually younger women have never had their blood pressure measured before becoming pregnant and may not attend for antenatal care until after 20 weeks gestation. If they are found to have raised pressures, it is difficult to be certain whether or not they have chronic hypertension or have gestational hypertension. In the developed world, perinatal mortality is now approaching 10 per 1000 women, and just under half of these deaths are the result of high blood pressure. Furthermore maternal mortality is about 50 deaths per million women and about 20% of these deaths can be attributed to all hypertensive diseases combined. In many cases of death as a result of eclampsia or pre-eclampsia (72% in one series), the care (diagnosis and management) was considered to have been substandard, with half of patients who died of eclampsia having had convulsions despite being admitted to obstetric wards (Figure 13.1). Figure 13.1 The hypertensive disorders of pregnancy. Several attempts have been made at classifying hypertension in pregnancy. None, however, is entirely satisfactory (Table 13.1). Table 13.1 Diagnostic criteria for the hypertensive syndromes in pregnancy The Working Group of the American National Heart, Lung and Blood Institute classifies hypertension in pregnancy as: Gestational hypertension becomes transient hypertension of pregnancy if pre-eclampsia is not present at the time of delivery and blood pressure returns to normal by 12 weeks after birth and chronic hypertension if high levels persist. There have been a great many attempts to define standardized criteria for the hypertensive syndromes in pregnancy. It has now become clear that gestational or pregnancy-induced hypertension (PIH) is not quite the innocent condition it was once thought to be. The peri-natal mortality in women with PIH is lower than in women with overt pre-eclampsia but is not as low as in women with persistently normal blood pressure. It is possible, therefore, that PIH is simply a mild form of pre-eclampsia. The main problem is pragmatic; if a woman develops de novo hypertension in late pregnancy but has no proteinuria, she will be classified as having gestational hypertension. If a week later she is found to have developed proteinuria, the diagnosis will be changed to pre-eclampsia. It is not possible to be sure whether a patient had gestational hypertension rather than pre-eclampsia until well into the puerperium (Table 13.2). Table 13.2 Problems with classification of hypertensive disorders of pregnancy There is the relatively new recognised syndrome of post-partum pre-eclampsia, where the blood pressure rises after delivery and proteinuria appears for the first time. The most benign category is pre-existing mild essential hypertension that is present before the 20th week of pregnancy, when the mother is assumed to have had pre-existing hypertension, although often no data are available. Many of these patients are overweight and are consuming a high salt diet. In these patients, blood pressure follows the normal pattern of pregnancy – it may fall during the first trimester and then increase again later in the pregnancy. This long-term hypertension is not confined to or caused by pregnancy, but it may be noted for the first time during pregnancy, typically towards the end. There is, however, an increased risk of developing super-added pre-eclampsia. Most women with secondary hypertension have an underlying renal disease (pyelonephritis, glomerulonephritis, reflux nephropathy). Older women with diabetes mellitus may have diabetic nephrosclerosis. Proteinuria or microproteinuria is usually present. Very rarely, young women may have renal artery stenosis due to fibromuscular dysplasia of the renal and other abdominal arteries. Adrenal causes of hypertension are rare at this age but episodic or very variable blood pressure suggests the diagnosis of phaeochromocytoma. Hypokalaemia not due to diuretics suggests a diagnosis of aldosterone excess. Aortic coarctation is a very rare cause of hypertension, which is classically seen in children or young people. All women of child-bearing age should have their blood pressure measured in the legs as well as the arms using a standard semi-automatic manometer. In the leg, the cuff is applied round the calf whilst the patient is lying flat. Pregnancy-induced hypertension develops after the 20th week of pregnancy and usually resolves within 10 days of delivery. This syndrome is common, occurring in up to 25% of first pregnancies, although it is less common (about 10%) in subsequent pregnancies. Some women who develop hypertension de novo early in the second half of pregnancy, however, are likely to progress to pre-eclampsia, with the development of proteinuria, thrombocytopenia and oedema and the need for early delivery. For diagnosis of pregnancy-induced hypertension to be made, the blood pressure must be documented to be normal before and after pregnancy. The International Society for the Study of Hypertension in Pregnancy defines pregnancy-induced hypertension as a single diastolic blood pressure (phase V) of 110 mm Hg or two readings of 90 mm Hg at least 4 h apart after the 20th week of pregnancy. The National High Blood Pressure Education Program of the United States defines pregnancy-induced hypertension as an increase >15 mm Hg in diastolic blood pressure or >30 mm Hg systolic blood pressure compared with readings taken in early pregnancy. Pregnancy-induced or gestational hypertension is not an entirely innocent condition. In a study of 703 consecutive pregnancies in primiparous women, those with PIH had smaller babies than normotensive women, although they were larger than those with pre-eclampsia (Table 13.3) Table 13.3 Birth weight and ponderal index in 703 consecutive primiparous women delivered at City Hospital, Birmingham. There were no perinatal deaths
Hypertension, pregnancy and the oral contraceptives
Pregnancy
Hypertension in pregnancy: An increasing problem
Blood pressure measurement
Maternal and perinatal mortality
Prevalence of hypertension
Hypertensive syndromes in pregnancy
Pre-eclampsia
Diagnosed on the basis of hypertension with a low platelet count or abnormal liver function tests. If these investigations are not available, the presence of proteinuria may be diagnostic. Ankle swelling is common in late pregnancy, not complicated by pre-eclampsia, and therefore is no longer considered to be a useful diagnostic feature.
Gestational and pregnancy-induced hypertension (PIH)
Blood pressure >140 mm Hg systolic blood pressure or >90 mm Hg diastolic blood pressure after 20 weeks in a woman who was normotensive before 20 weeks’ gestation
Hypertension should be confirmed by two separate measurements
Proteinuria
300 mg/l protein or 30 mg/mmol creatinine in a random specimen or total protein excretion of 300 mg/24 h. This is no longer considered to be a reliable marker for pre-eclampsia as false positive results can occur if the specimen is not clean catch or there has been a recent urinary tract infection. Proteinuria is present in most chronic renal diseases
Chronic hypertension
Blood pressure 140/90 mm Hg or more before 20th week of pregnancy or hypertension in late pregnancy, persisting 6 weeks after delivery. Some of these patients have underlying (usually renal) causes of their hypertension.
Pre-eclampsia superimposed on chronic hypertension
Regarded as highly likely in women with hypertension alone who develop a low platelet count and/or abnormal liver function tests or new-onset proteinuria or in women with pre-existing hypertension and proteinuria who have sudden increases in blood pressure or proteinuria, thrombocytopenia or increases in hepatocellular enzymes
Blood pressure is not measured before pregnancy in many women, and some may have had previous undiagnosed hypertension.
Blood pressure tends to settle in mid-pregnancy.
Differentiation between mild pre-eclampsia and less ominous rises in blood pressure in late pregnancy is difficult. The differentiation between PIH and pre-eclampsia can often only be decided after the pregnancy is over.
Whether increases in blood pressure in late pregnancy may proceed rapidly to severe pre-eclampsia cannot be predicted.
Blood pressure may rise de novo after delivery of the baby in a syndrome similar to pre-eclampsia.
Many women are opting for later pregnancies and may have essential hypertension.
Ambulatory blood pressure monitoring is being used increasingly for the various forms of hypertension in pregnancy.
Pre-Existing Hypertension (Essential Hypertension)
Pre-Existing Hypertension (Secondary Hypertension)
Pregnancy Induced Hypertension
