We thank Obara et al. for their interest in our study and for presenting us with data from the Tohoku Medical Megabank Project Birth and Three-Generation (TMM BirThree) Cohort Study [1]. Both studies reliably confirmed that the use of nifedipine in patients with hypertensive disorders of pregnancy was increasing in Japan. Since their results were equivalent to those of our study, we believe that their data confirmed the robustness of our study.

Our data from the Japan Medical Data Center (JMDC) claims database, however, showed a slightly higher proportion of antihypertensive drug use than that reported by the TMM BirThree cohort study. This may be because of the gap between the use and prescription of the medication, as stated by Obara et al. Administrative claims data, especially for patients in early pregnancy, may also have included prescriptions that were discontinued due to pregnancy. However, in terms of assessing trends, we believe that their data showed similar results and confirmed the applicability of the administrative claims data.

We agree with Obara et al. about the recent interesting application of amlodipine in the treatment of hypertensive disorders during pregnancy. We believe that a study on the pregnancy outcomes of patients treated with amlodipine is feasible using the JMDC database. Several studies have already evaluated the safety of other medications during pregnancy using the JMDC database [2, 3]. However, this database does not include data on blood pressure or laboratory examinations—a general limitation of administrative claims data. It is, therefore, not feasible to evaluate the efficacy of medications with blood pressure-lowering effects using such data.