Objective It is unclear whether established risk factors for pre-eclampsia are related to blood pressure (BP) changes across pregnancy in women who do not develop pre-eclampsia. We investigated these associations.

Methods We studied routine antenatal BP measurements for 11 789 women (median 14 per woman) in ALSPAC who had a live term birth without pre-eclampsia or previous hypertension. Linear spline random effects models with knots at 18, 30 and 36 weeks gestation described changes in BP with gestational age.

Results On average systolic BP (SBP) and diastolic BP (DBP) decreased until 18 weeks and then rose, with increasing rate at 30 and then again at 36 weeks. BP was higher at 8 weeks for obese women compared with normal weight women, nulliparas compared with multiparas, and for never-smokers compared with women who smoked throughout pregnancy or in the first trimester only. Women who smoked throughout pregnancy had consistently lower BP while women who smoked only in the first trimester attained a similar BP trajectory to never-smokers in late pregnancy. BP rose more slowly between 18 and 30 weeks and more rapidly between 30 and 36 weeks in obese women than in normal weight women. Nulliparous women had faster rises in DBP from 30 weeks and SBP from 36 weeks than multiparous women and twin pregnancies were associated with faster rises in BP from 30 weeks.

Conclusion Established pre-eclampsia risk factors are associated with the pattern of BP changes in healthy pregnancy, suggesting that they affect BP change across the whole distribution.