Background
Chronic maternal hypertension is associated with a 3- to 5-fold increased risk of preeclamspia. The compounding effect of additional risk factors on both preeclampsia prevalence and pregnancy outcome in such patients is uncertain. We hypothesised there may be significant clinical risk factors identifiable in early pregnancy within this cohort which are associated with an increased risk of preeclampsia. If so, early risk stratification may help guide management and intervention to attenuate this risk.
Methods
Clinical risk factors for preeclampsia identified at the pregnancy booking visit in women with known chronic hypertension were obtained from two centres in Melbourne, Australia in a retrospective analysis of 42,500 singleton deliveries (2008-2018). Risk factors included age, parity, previous preeclampsia, ethnicity, smoking, secondary hypertension, renal disease/proteinuria, hypertension duration, diabetes, antihypertensive use at conception and/or first trimester, aspirin use before 16 weeks, blood pressure (BP) at booking, and body mass index (BMI). Associations were evaluated by univariate and multivariate logistic regression analysis, with significance p<0.05.
Results
233 births occurred in 186 women with chronic hypertension (0.55% prevalence). Preeclampsia occurred in 36 (15.5%) of these births, of which 19 (8.2%) were severe preeclampsia. On univariate analysis, previous preeclampsia [OR 5.45 (1.89-12.71)] and hypertension duration [OR 2.4 (1.76-4.92)] were most strongly associated with preeclampsia of any severity. Adjusting for age, parity, previous preeclampsia, BMI, BP and renal disease, hypertension duration >5 years remained an independent risk factor [OR 1.23 (1.03-1.48)]. For severe preeclampsia, strongest associations were maternal age >35, renal disease, BMI <30 and previous preeclampsia, the last remaining significant after adjustment [OR 13.2 (1.47-119.6)].
Conclusion
Preeclampsia risk in pregnant women with chronic hypertension is high, and historical features such as previous preeclampsia or a longer duration of hypertension may pose additional risk. This highlights the importance of pre-pregnancy counselling and careful clinical appraisal in early pregnancy in women with chronic hypertension to best direct appropriate gestational management.