Objective: To establish the profiles of 24-h non-invasive ambulatory blood pressure measurement (ABPM) during the trimesters of pregnancy and the puerperium in normotensive healthy primigravidae.
Design: A prospective study in which 24-h ABPM was performed on five occasions in each subject: in the first trimester between 9 and 16 weeks' gestation; in the second trimester between 18 and 24 weeks; in the third trimester between 26 and 32 weeks and between 33 and 40 weeks; and finally at 6 weeks post partum.
Method: One hundred and six Caucasian primigravid women who were normotensive at their first booking visit were recruited consecutively from the antenatal clinic and had 24-h ABPM performed with the SpaceLabs 90207 ambulatory system.
Results: Of the 106 women recruited, 98 completed 24-h ABPM on four of the five measurement occasions. Four women delivered prematurely before 33 weeks' gestation, thereby missing one ABPM measurement. Changes during pregnancy and the puerperium were assessed against the ABPM performed in the first trimester. There was no difference for daytime or night-time systolic blood pressure between 9 and 33 weeks, but it rose significantly from 33 to 40 weeks. At 6 weeks post partum, systolic blood pressure was not significantly different from the daytime pressure in the first-trimester ABPM but was raised significantly at night. Diastolic blood pressure decreased significantly between 18 and 24 weeks for both daytime and night-time. From 33 to 40 weeks it increased in parallel with systolic blood pressure, and at 6 weeks post partum it was raised significantly compared with first-trimester values for daytime and night-time. The nocturnal fall in blood pressure was preserved throughout pregnancy with a significant difference between daytime and night-time measurements present on all measurement occasions for systolic, diastolic and mean blood pressures and heart rate. There were significant differences between daytime ABPM and clinic blood pressure for both systolic and diastolic blood pressure up to 33 weeks. From 33 weeks until 6 weeks post partum there was no significant difference between daytime ambulatory and clinic blood pressures.
Conclusion: This study provides reference values for ABPM in healthy primigravidae with generally uncomplicated pregnancies.