Seasonal variation in home blood pressure during pregnancy and frequency of hypertensive disorders of pregnancy: a multicenter prospective study of home blood pressure measurements in pregnant women using information technology.

This multicenter prospective study investigated seasonal variation in home blood pressure (HBP) during pregnancy and its association with the frequency of hypertensive disorders of pregnancy (HDP) and developed trimester-specific upper limits of HBP according to season. Low-risk women with singleton pregnancies were recruited at six university hospitals and three maternity clinics. HBP was measured by a sphygmomanometer twice daily and recorded online using a mobile application. HBP was evaluated according to season (winter, spring, summer, and autumn) and gestational age. Of 705 women recruited, 603 were finally included. Mean diastolic HBP values were lowest in summer and highest in winter throughout pregnancy (mean difference between summer and winter, 3.5-4.6 mmHg). Mean systolic HBP values were also lowest in summer and highest in winter except during the early period of the second trimester (mean difference between summer and the season with the highest value, 2.5-3.4 mmHg). HDP was diagnosed in 32 women (5.3%). The risk of HDP was significantly higher in women who delivered in spring and autumn but not in winter compared with summer. The rounded upper limit of HBP was 120/80 mmHg in the first trimester, 120/75 mmHg in the second trimester, and 125/80 mmHg in the third trimester for summer and 125/85 mmHg, 125/80 mmHg, and 130/85 mmHg, respectively, for other seasons. Systolic and diastolic HBP were lowest in summer throughout pregnancy. Seasonal variation should be considered when interpreting HBP and the risk of HDP during pregnancy.