OBJECTIVES: To investigate whether the upper home blood pressure reference limit in healthy pregnant women correspond to 135/85 mmHg as used when diagnosing white coat hypertension outside pregnancy.

METHODS: In this prospective observational study 103 healthy, singleton pregnant women with a mean age of 32 ± 4 (±SD) years and with a median pre-pregnancy body mass index of 21 (interquartile range 20-24) kg/m were included. Home blood pressure was measured with the device Microlife® BP 3A Plus twice daily for three days (18 measurements in total) in addition to routine office blood pressure measurements in early (median 12 (weeks)), mid (20) and late pregnancy (35). Upper blood pressure reference limits were calculated as mean +2 SD.

RESULTS: Office blood pressure versus home blood pressure were 115 ± 11/72 ± 7 versus 103 ± 7/64 ± 5 mmHg in early pregnancy, 112 ± 11/74 ± 7 versus 102 ± 7/63 ± 5 mmHg in mid pregnancy and 118 ± 11/75 ± 8 versus 107 ± 8/66 ± 6 mmHg in late pregnancy. The mean difference between office blood pressure and home blood pressure was 10 mmHg. In late pregnancy, the upper reference limit was 140/91 mmHg for office blood pressure and 123/78 mmHg for home blood pressure with slightly lower values in early and mid pregnancy, respectively.

CONCLUSION: In late pregnancy, the upper home blood pressure reference limit in a population of healthy women was 123/78 mmHg. This value questions the generally proposed level of 135/85 mmHg to define white coat hypertension in pregnancy.