Objectives when defining preeclampsia

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Clinician's perspective

Like any diagnostic ''test,'' the definition of preeclampsia ultimately classifies women as having or not having the condition. Once labeled as pre-eclampsia, a treatment threshold is crossed, triggering a series of changes in clinical management. The criteria used to classify pre-eclampsia have, therefore, significant implications for clinical care.

The objectives of defining pre-eclampsia are twofold:

1. to identify women and their babies with severe maternal or fetal complications due to pre-eclampsia; and

2. to identify women at significant risk of subsequently developing severe maternal and/or fetal sequelae due to pre-eclampsia who require more intensive monitoring and timely delivery to prevent these problems.

Defining pre-eclampsia by the most common early manifestations of the syndrome (hypertension and proteinuria), clusters a broad range of clinical scenarios, from mild disease posing no immediate threat to maternal or fetal health through to women with eclampsia, severe liver and renal dysfunction associated with a coagulo-pathy and/or severe fetal compromise. For some these severe complications are present at the time of diagnosis, others develop them in the ensuing days or weeks. For many, pre-eclampsia never progress beyond the initial manifestations of mild disease. Thus the current definitions of pre-eclampsia function in dual capacity, as a diagnostic tool for severe maternal or fetal disease and as a screening test that identifies women at significant risk of subsequently developing severe sequelae of pre-eclampsia.

Like all screening tests, sensitivity and specificity are balanced around the cut-off criteria utilized. No definition is perfect, but the object is to identify all women who develop severe disease (high sensitivity) and exclude all at minimal risk of significant sequelae (high specificity). If the definition is too broad, an inclusive approach will result in the diagnosis of women with very mild disease. Classifications that included the criteria of edema (Anonymous, 1990; Hughes, 1972) or an isolated rise in blood pressure with the final blood pressure remaining less than 140/90 mmHg (Anonymous, 1990), resulted in labeling many women with pre-eclampsia who were at little risk of serious maternal or fetal morbidity. An isolated rise in blood pressure has now been shown to occur in 27—67% of pregnancies, and identifies women who have an essentially normal pregnancy outcome (North et al., 1999; Ohkoshi et al., 2003; Villar and Sibai, 1989). A further study reported no increase in important adverse outcomes among the 2% of nulliparous women with proteinuria and a 15 mmHg rise in diastolic blood pressure, but whose blood pressure remained less than

90 mmHg (Levine et al., 2000). An isolated rise in blood pressure and the presence of edema have now been dropped from recent classifications (Anonymous, 2000, 2002; Brown et al., 2000; Helewa et al., 1997).

Equally, if criteria are too stringent, then some women who are at risk of developing severe maternal disease will not be identified and appropriate management not implemented. Redman and Jefferies found that if more strict criteria for hypertension (a rise in diastolic blood pressure of at least 25 mmHg to at least 90 mmHg) were employed, this identified pregnancies with increased rates of proteinuria, lower birthweights and increased perinatal mortality (Redman and Jefferies, 1988). These criteria for hypertension were shown to be associated with a higher rate of small for gestational age babies than if an absolute BP cut-off was utilized (Perry and Beevers, 1994). Redman's criteria have been used in major clinical trials (CLASP, 1994) but have not been widely accepted in clinical practice. The reason for this includes the requirement of an early blood pressure to make the diagnosis. This is not available in a significant number of pregnancies, especially in certain sectors where women often present late in pregnancy. This definition also excludes women with proteinuria combined with a diastolic blood pressure greater than 90 mmHg, but whose increase in blood pressure is less than 25 mmHg. Amongst these women, the precise number who would develop severe maternal or fetal complications is unknown. As several million pregnancies are complicated by pre-eclampsia annually, failure to recognize even a small percentage translates into large numbers of women potentially placed at risk globally.

The current classifications of gestational hypertension and pre-eclampsia do identify two groups of women with very different risk profiles (Figure 17.1) (Brown and Buddle, 1995a; North et al., 1999). US-based studies also report fewer major adverse maternal or fetal in gesta-tional hypertension compared with pre-eclampsia (Barton et al., 2001; Hauth etal., 2000). It should be severe hypertension severe hypertension

multi-system complications

multi-system complications

Gestational hypertension

Pre-eclampsia

Figure 17.1 Among women with gestational hypertension and pre-eclampsia, the proportion who develop severe hypertension or multi-system complications. Multi-system complications included renal insufficiency, thrombocytopenia, liver dysfunction, imminent eclampsia, eclampsia and pulmonary edema. □, North et al. (1999); Brown and Buddle (1995a).

recognized that within the gestational hypertension group, there are small subgroups of women at relatively greater risk of morbidity. These include those with severe hypertension (Hauth et al., 2000) and those with early-onset disease (Barton et al., 2001; Saudan et al., 1998).

The Australasian definition, with its emphasis on a systematic approach to determine if the woman has multisystem involvement or if her baby's health is adversely affected, can be readily applied to clinical practice (Figure 17.2). After determining whether a woman has gestational hypertension, a systematic review should be undertaken for symptoms and signs, with supportive evidence from laboratory investigations or ultrasound scan, of maternal multisystem disease and adverse fetal/ placental outcomes. According to the ASSHP classification, if these are present, the woman has pre-eclampsia and if they are absent she has gestational hypertension. This approach can also be applied in the daily assessment of women with pre-eclampsia who are being conservatively managed in an attempt to increase gestational age at birth.

Research perspective

In contrast to clinical obstetrics where the classification needs to be inclusive, for most research it is preferable that only women with definite disease are studied. This applies particularly to basic research into the pathogenesis of the condition. It remains contentious as to whether the researcher should insist on proteinuria to make the diagnosis of pre-eclampsia (Anonymous, 2002) or whether women with gestational hypertension and no proteinuria but other manifestations of multisystem disease are included (Brown et al., 2000). This decision remains with the researcher.

Recent studies have highlighted the variable often poor quality definitions used in studies on pre-eclampsia (Chappell et al., 1999; Harlow and Brown, 2001). In particular, almost a third of studies provided no definition and up to a fifth of papers relied on urinary dipstick to determine proteinuria. The sine qua non is that the definition of the condition be provided when performing research on pre-eclampsia. Given the limitations of urinary dipstick to determine proteinuria, as described

Gestational Hypertension de novo hypertension after 20 weeks diastolic BP >90 mmHg and/or systolic BP>140 mmHg

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