Response to Detection of Midpregnancy Fall in Blood Pressure by Out-of-Office Monitoring
Metoki et al1 commented on our recent publication on the absence of a midpregnancy fall in diastolic blood pressure (BP) in women with a low educational level.2 They noticed that, in our study population, there was no midpregnancy fall in systolic BP and that the midpregnancy fall in diastolic BP was relatively small. Metoki et al1 attributed this to few measurement points during pregnancy. We acknowledge that, because we were limited to 3 measurement points during pregnancy, we could not account for circadian and daily variations in BP. However, as discussed in our article, this limitation probably resulted in random measurement error. For measurement error to underestimate a midpregnancy fall in BP, BP in early pregnancy would have to have been systematically underestimated, and that in midpregnancy would have to have been systematically overestimated; this seems unlikely.
Regarding the pattern of change in systolic BP during pregnancy, previous studies have provided inconsistent results. In 235 normotensive pregnant women, Hermida et al3 observed a midpregnancy fall in both systolic and diastolic BPs. In contrast, Halligan et al,4 who analyzed ambulatory BP measurements from 98 primigravid women, found an average decrease of 1 mm Hg in daytime diastolic BP between the first and second trimester but observed no such fall in systolic BP.
Metoki et al1 proposed home BP monitoring to study changes in BP during gestation. Using home BP measurements from 101 pregnancies, they demonstrated that the timing and amplitude of the midpregnancy fall in BP may vary by the season in which delivery is predicted.5 However, when this seasonal variation was not taken into account, they found an average fall in diastolic BP of ≈2 mm Hg. Taking into account that hypertensive pregnancies were excluded from their analyses, these results compare well with those presented in our article.
Although we believe that home BP measurements would improve the precision of these measurements, this method seems less feasible in a large cohort study, such as the Generation R Study. It would lead to substantial burden to participants and a large dependence on their compliance. We, therefore, recommend home BP monitoring in smaller cohort studies.
Sources of Funding
This work was supported by Erasmus MC, University Medical Center Rotterdam, Erasmus University Rotterdam, and The Netherlands Organization for Health Research and Development, as well as The Netherlands Organization for Scientific Research (grant 017.002.107).
Metoki H, Ohkubo T, Sato Y, Kawaguchi M, Nishimura M, Watanabe Y, Imai Y. Detection of midpregnancy fall in blood pressure by out-of-office monitoring. Hypertension. 2009; 53: e12–e13.
Silva LM, Steegers EA, Burdorf A, Jaddoe VW, Arends LR, Hofman A, Mackenbach JP, Raat H. No midpregnancy fall in diastolic blood pressure in women with a low educational level: the Generation R Study. Hypertension. 2008; 52: 645–651.
Hermida RC, Ayala DE, Iglesias M. Predictable blood pressure variability in healthy and complicated pregnancies. Hypertension. 2001; 38: 736–741.
Metoki H, Ohkubo T, Watanabe Y, Nishimura M, Sato Y, Kawaguchi M, Hara A, Hirose T, Obara T, Asayama K, Kikuya M, Yagihashi K, Matsubara Y, Okamura K, Mori S, Suzuki M, Imai Y, and the BOSHI Study Group. Seasonal trends of blood pressure during pregnancy in Japan: the Babies and their Parents’ Longitudinal Observation in Suzuki Memorial Hospital on Intrauterine Period Study. J Hypertens. 2008; 26: 2406–2413.