Furthermore, the early-pregnancy level and the average
change in blood pressure have been found to differ by
maternal prepregnancy BMI, smoking and parity [10,13,14],
even among women who then experienced a healthy birth
outcome [10]. This would imply that different trajectories of
blood pressure may be healthy for different subgroups of
women. However, differences in blood pressure trajectories
by maternal age and education were much smaller
[10]. It is also plausible that the normal trajectory may
depend on the initial level of blood pressure, as a greater
increase is likely to be tolerable for a woman who begins
pregnancy with a relatively low blood pressure. Establishing
blood pressure reference ranges across pregnancy for
different subgroups of women, who do not experience
adverse health outcomes, may provide important information
about what is normal at different gestational ages