Elevated diastolic blood pressure until mid-gestation is associated with preeclampsia and small-for-gestational-age birth: a population-based register study

BACKGROUND: Gestational hemodynamic adaptations, including lowered blood pressure (BP) until mid-gestation, might benefit placental function. We hypothesized that elevated BP from early to mid-gestation increases risks of preeclampsia and small-for-gestational-age birth (SGA), especially in women who also deliver preterm (< 37 weeks). METHODS: In 64,490 healthy primiparous women, the change in systolic and diastolic BP from early to mid-gestation was categorized into lowered (≥ 0 mmHg decreased), and elevated (≥ 1 mmHg increase). Women with chronic hypertension, chronic renal disease, pre-gestational diabetes and systemic lupus erythematosus were excluded. Risks of preeclampsia and SGA birth were estimated by logistic regression, presented with adjusted odds ratio (aOR) and 95% confidence intervals (CI). Further, the effect of BP change in combination with stage 1 hypertension (systolic BP 130-139 mmHg or diastolic BP 80-89 mmHg) in early gestation was estimated. RESULTS: Compared to women with lowered diastolic BP from early to mid-gestation, those with elevated diastolic BP had increased risks of preeclampsia (aOR: 1.8 [1.6-2.0]) and SGA birth (aOR: 1.3 [1.2-1.5]). The risk estimates were higher for preeclampsia and SGA when combined with preterm birth (aORs: 2.2 [1.8-2.8] and 2.3 [1.8-3.0], respectively). The highest rate of preeclampsia (9.9%) was seen in women with stage 1 hypertension in early gestation and a diastolic BP that was elevated until mid-gestation. This was three times the risk, compared to women with normal BP in early gestation and a diastolic BP that was decreased until mid-gestation. The association between elevated systolic BP from early to mid-gestation and preeclampsia was weak, and no significant association was found between changes in systolic BP and SGA births. CONCLUSION: Elevated diastolic BP from early to mid-gestation was associated with increased risks of preeclampsia and SGA, especially for women also delivering preterm. The results may imply that the diastolic BP starts to increase around mid-gestation in women later developing placental dysfunction disorders.