pressure has deviated from the normal trajectory may
provide additional information about risk. Nevertheless,
subgroups of women who are known to be at a higher risk
of adverse perinatal outcomes should be considered as
such, even with blood pressure within the normal range.
Our reference ranges also show differences of around
5mmHg in SBP and DBP between 20 weeks and delivery,
suggesting that using different blood pressure thresholds at
different gestational agesmay improve the identification of
women with abnormal trajectories.
There has been much research in the area of foetal
growth charts [29–31], and more recently customized charts
that are dependent on maternal characteristics [20]. Routine
measurements of symphysis-fundal height and ultrasound
scan measurements of foetal size may be compared against
these charts and used to identify growth-restricted foetuses
[32,33]. There may be potential for blood pressure charts in
pregnancy to be used in conjunction with foetal growth
charts to aid in the identification of pregnancies at risk of
SGA infants, as high blood pressure and greater increases in
blood pressure are associated with reduced offspring birthweight
[11,12]. In addition, blood pressure reference ranges
may help to identify women who are at risk of preeclampsia
and delivering preterm. We have previously shown in this
cohort [34] and others elsewhere [23] that the increase in
blood pressure is steeper in preeclamptic than in normotensive
pregnancies. Thus, preeclamptic women would be
expected to deviate from the normal pattern of change,
although the potential for deviations from the normal
trajectory to be used in prediction of adverse outcomes
remains to be assessed.
We conclude that the normal pattern of change in blood
pressure across gestation, for a healthy term pregnancy
resulting in an appropriate sized infant, differs by maternal
subgroups. There may be potential to use whole population
and stratified normal reference ranges such as these
in screening for women with abnormal trajectories, which
may be indicative of potential adverse pregnancy outcomes
such as preeclampsia, preterm birth and SGA offspring.
However, the value of this will require evaluation
through the development and validation of prediction
models.