Epidemiological studies regarding hypertensive disorders of pregnancy: A review

A hypertensive disorder of pregnancy (HDP) is defined as hypertension emerging after 20 weeks of gestation and resolving up to 12 weeks post‐partum, and occurs in about 5% of all pregnancies. Complications associated with HDP have poor prognoses, and maternal deaths attributable to HDP are predicted to exceed 70 000 per year worldwide. Understanding the pathogenesis and risk factors of hypertensive disorders of pregnancy is important, and they are often investigated in observational studies. Given that therapeutic interventions cannot be controlled in observed studies, it is necessary to interpret which factors correspond to exposure and which factors correspond to confounding and intermediate factors in each study. From the Babies and their parents' longitudinal observation in the Suzuki Memorial Hospital on Intrauterine period study, blood pressure in early pregnancy was not only predictive of a child's birthweight, but the trajectory was also associated with the birthweight. From the larger‐scale birth cohort studies currently conducted in Japan will provide the novel potential risk factors of hypertensive disorders of pregnancy and preventive strategies of them. In Japan, observational or intervention studies are just beginning to emerge. The continuation of both a distinctive cohort and a large cohort is needed, and the development of good quality intervention trials based on the results of observational studies is important.