Hypertensive disorders in pregnancy and hypertension in later life

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There is more information about the risk of hypertension in later life and previous pre-eclampsia than any other long-term outcome.

This is probably because hypertension is relatively common in younger women. Relatively young women remain the focus for most of these studies for the pragmatic reason that computerized databases of pregnancy outcome are relatively recent and represent the most convenient way for initiating large-scale longitudinal studies, due to the expense of dedicated prospective observational studies.

Wilson et al. described the long-term outcome for a cohort of women delivering in Aberdeen, Scotland between 1951 and 1970 (Wilson et al., 2003). Women were classified into normotensive, gestational hypertension (i.e. hypertension without proteinuria) and pre-eclampsia (i.e. hypertension with proteinuria). Hypertension in later life was ascertained by questionnaire and physical examination of respondents within the cohort. While this is open to recall bias and respondent bias, the cohort was also linked to computerized databases of hospital discharge data and death certificate data. There were associations between both gestational hypertension and pre-eclampsia and later hypertension both by questionnaire and physical examination of respondents and by linkage of the whole cohort to hospital discharge data. The relative risks were in the region of 2—4.

A large-scale prospective cohort study of women recruited to the control group of a matched cohort study of the oral contraceptive pill related a previous diagnosis of pre-eclampsia to the risk of later chronic hypertension. The authors described a relative risk of 2.4 (2.1—2.6). However, the criteria for diagnosis of pre-eclampsia were not defined and it is likely that this group included many women with misclassified hypertension (Hannaford et al., 1997).

A matched cohort study of 273 women with well-defined hypertensive disorders of pregnancy demonstrated associations between both gesta-tional hypertension and pre-eclampsia and later chronic hypertension. The incidence was 45% in the pregnancy-induced hypertension group and 14% in controls (P < 0.001) This study correctly excluded women where the data were lacking to classify the pregnancy-related hypertension, due to missing data or late booking. Interestingly, there was no association between eclampsia and later hypertension, although only 29 women were followed up who had experienced this event (Marin et al., 2000).

Sibai and colleagues describe prospective follow-up of 179 women who experienced eclampsia but did not have pre-existing hypertension (Sibai et al., 1992). They demonstrated that the likelihood of hypertension in later life depended on the gesta-tional age where the index event took place: 18% if eclampsia occurred <31 weeks, 12% if eclampsia occurred between 31 and 36 weeks and 5% if eclampsia occurred at term. This trend is statistically significant (P = 0.03 by chi square test for trend — not reported by authors). They also found that women who had pre-eclampsia in subsequent pregnancies had a greater risk of later hypertension than women whose subsequent pregnancies were not affected by pre-eclampsia (25% versus 2%, P< 0.0001).

The same authors had earlier reported a matched cohort study of 406 women aged < 26 years who developed severe pre-eclampsia during their first pregnancy. The diagnostic criteria employed were strict and women with unclassifi-able hypertension were excluded. The incidence of chronic hypertension was 15% compared with 6% in the control group and the difference was highly statistically significant (Sibai et al., 1986).

The studies described above strongly suggest that both pre-eclampsia and eclampsia are related to the risk of chronic hypertension in later life. Use of strict diagnostic criteria means that some of these studies cannot be explained by misclassifica-tion. The relationship between gestational age at the time of the eclamptic event and the risk of later hypertension does suggest heterogeneity within this group and that long-term implications of a diagnosis of pre-eclampsia or eclampsia might vary according to the gestational age at onset in the affected pregnancy.

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