Prediction of pregnancy-induced hypertension by a shift of blood pressure class according to the JSH 2009 guidelines

Elevated blood pressure (BP) at early or mid pregnancy is a known risk factor for pregnancy-induced hypertension (PIH). However, the association between BP changes during the first half of pregnancy and subsequent PIH development is unknown. We used changes in maternal BP between 16 and 20 weeks of gestation to evaluate the risk of PIH. A total of 976 pregnant women with BP estimations recorded before 16 weeks and at 20 weeks of gestation participated in this study. BPs were classified by the Japanese Society of Hypertension 2009 Hypertension Treatment Guidelines (JSH 2009). There was a significant trend for future PIH in women whose JSH 2009 BP class increased between 16 and 20 weeks of gestation, and the risk of PIH was highest among women whose BP was Class IV Hypertension (systolic BP⩾140 mm Hg and/or diastolic BP⩾90 mm Hg). The risk of PIH increased in women whose BPs shifted from Classes I Optimal (systolic BP<120 mm Hg and diastolic BP<80 mm Hg) and II Normal (systolic BP 120–129 mm Hg and/or diastolic BP 80–84 mm Hg) before 16 weeks to Class III High-Normal (systolic BP 130–139 mm Hg and/or diastolic BP 85–89 mm Hg) at 20 weeks of gestation. These shifts in BP class were significantly correlated with the risk of PIH after adjustments for variables (P-value for trend <0.05). Within JSH 2009 Classes I, II and III, a shift in BP from a low to a high class between 16 and 20 weeks of gestation predicts the subsequent development of PIH.