Objective: To determine the magnitude of Phase IV-V diastolic blood pr
essure differences in human pregnancy. Methods: Blood pressure was mea
sured by a standardized technique, using a Hawkesley random zero sphyg
momanometer, in 221 pregnant women. Measurements were made in the seco
nd and third trimesters of pregnancy. The study included a number of w
omen with chronic hypertension and a number with preeclampsia. Main Ou
tcome Measures: Magnitude of Phase IV-V differences in normal and hype
rtensive pregnant women. Results: As expected, values for Phase V dias
tolic blood pressure were lower than for those for Phase IV both in th
e second and in the third trimesters of pregnancy. In the third trimes
ter, the median difference between Phase IV and V Korotkoff sounds was
5 mm Hg in normals, 7 mm Hg in chronic hypertensives, and 5 mm Hg in
women with preeclampsia. Conclusion: These differences are within the
error of the measurements as made in clinical practice. The smallest d
ifferences were found in women with preeclampsia, who are likely to pr
ovide the practitioner with the most difficult management decisions.