The timing of chronic hypertension onset in pregnancy was not associated with the severity of superimposed preeclampsia

Chronic hypertension is a significant risk factor for developing preeclampsia, also called superimposed preeclampsia. In pregnancy, chronic hypertension is defined as elevated blood pressure before pregnancy or before 20 weeks of gestation. However, whether the onset time of chronic hypertension influences the risk of developing preeclampsia and the severity remains unclear. A total of 478 pregnant women with chronic hypertension were included and divided into two distinct groups: those who developed superimposed preeclampsia and those who did not. Data, including age, BMI, and the onset time of chronic hypertension, were collected. We compared women with different timing of chronic hypertension onset with respect to later development and severity of superimposed preeclampsia. 281(59 %) women did not develop preeclampsia later, while 197 (41 %) did. No significant differences were observed in maternal age, BMI, and duration of chronic hypertension between the two groups. A significantly higher incidence of superimposed preeclampsia was observed in women with pre-existing chronic hypertension. However, the severity, including the number of severe and early-onset preeclampsia and the number of preterm births, did not differ between the two groups. 24 (12.2 %) women developed recurrent preeclampsia, which was not related to the timing of chronic hypertension onset. Although women with pre-existing chronic hypertension are at greater risk of superimposed preeclampsia, our findings suggest that once chronic hypertension is present, the onset time may not significantly alter the clinical outcomes of preeclampsia. Our findings highlight the importance of managing women with chronic hypertension in pregnancy, regardless of the timing of onset.