Antenatal blood pressure change by BMI category: Analysis using data from the Born in Bradford cohort

Publication authors

Farrar D.; Santorelli G.; Lawlor D.; Macdonald-Wallis C.; Tuffnell D.; Sheldon T.


Introduction The prevalence of hypertensive disorders of pregnancy (HDP) (hypertension and pre-eclampsia) are increasing and are leading causes of maternal and perinatal morbidity and mortality. Increased BMI is a risk factor and evidence from one study suggests that it is also associated with patterns of systolic and diastolic blood pressure (SBP and DBP) change from early pregnancy, but this needs further replication. Objective Determine the association of early pregnancy BMI categories with BP change through pregnancy and with HDP.

Methods Multilevel linear spline models with five parameters (‘knot point’s’ at 8, 8-24, 24-30, 30-36, >36 weeks of gestation) and prevalence estimates of HDP were estimated for each BMI category

Results 10 535 women were included. There were marked differences in mean DBP and SBP at 8 weeks of gestation with underweight women having the lowest levels and obese the highest. Mean difference in SBP at eight weeks and >36 weeks for underweight, overweight and obese, compared to normal weight women was -5.631 (-5.662 to 5.601) and -4.377 (-4.489 to 4.266), 4.393 (4.378-4.408) and 3.574 (3.523-3.626), 10.924 (10.909-10.940) and 8.390 (8.333-8.447) respectively. Mean difference in DBP at 8 and >36 weeks for underweight, overweight and obese, compared to normal weight women was -3.388 (-3.405 to 3.372) and -2.584 (-2.685 to 2.483), 3.034 (3.025-3.042) and 2.673 (2.627-2.720), 8.499 (8.490-8.507) and 6.132 (6.081-6.184) respectively. Patterns of change over pregnancy were broadly similar by BMI category. By the end of pregnancy the differences between categories was smaller than at the start of pregnancy. Both gestational hypertension and pre-eclampsia prevalence increased across all BMI categories from underweight to obese. For underweight, normal weight, overweight and obese women the prevalence of gestational hypertension was 6.1% (95% CI: 4.0- 8.5), 11.4% (CI: 10.5-12.3), 17.1% (CI: 16.1-18.5) and 33.5% (CI: 31.5-35.5) and the prevalence of pre-eclampsia was 3.5% (CI: 2.1- 5.7), 5.3% (CI: 4.7-6.0), 8.6% (CI: 7.6-9.7) and 21.0% (CI: 19.0- 22.7) respectively.

Conclusion We confirm the association of BMI categories with both gestational hypertension and pre-eclampsia. We have also shown marked differences in mean BP at the start of pregnancy which remains throughout, but tends to narrow by the end of pregnancy.