International gestational age-specific centiles for blood pressure in pregnancy from the INTERGROWTH-21st Project in 8 countries: a longitudinal cohort study
GREEN L., KENNEDY S., Mackillop L., GERRY S., purwar M., STAINES URIAS E., Cheikh Ismail L., barros F., cesar V., carvalho M., Ohuma E., jaffer Y., NOBLE J., gravett M., pang R., LAMBERT A., bertino E., PAPAGEORGHIOU A., garza C., bhutta Z., Villar J., WATKINSON P.
Background Gestational hypertensive and acute hypotensive disorders are associated with maternal morbidity and mortality worldwide. However physiological blood pressure changes in pregnancy are insufficiently defined. We describe blood pressure changes across healthy pregnancies from the INTERGROWTH-21st Fetal Growth Longitudinal Study to produce international, gestational age-specific, smoothed centiles (3rd, 10th, 50th, 90th and 97th) for blood pressure. Methods and findings Secondary analysis of a prospective, longitudinal, observational cohort study (2009-16) across 8 diverse urban areas in Brazil, China, India, Italy, Kenya, Oman, United Kingdom, and United States. We enrolled healthy women at low risk of pregnancy complications. We measured blood pressure, using standardised methodology and validated equipment at enrolment (<14 weeks), then every 5±1 weeks until delivery. We enrolled 4607 (35%) women of 13108 screened. The mean maternal age was 28·4 (SD 3·9) years; 97% (4204/4321) of women were married or living with a partner, and 68% (2955/4321) were nulliparous. Their mean BMI was 23·3 (SD 3·0) kg/m2. Systolic blood pressure was lowest at 12 weeks, median 111.5 (95% CI 111·3 to 111·8)mmHg, rising to a median maximum of 119·6 (95% CI 118·9 to 120·3)mmHg at 40 weeks’ gestation, a difference of 8·1 (95% CI 7·4 to 8·8)mmHg. Median diastolic blood pressure decreased from 12 weeks, 69·1 (95% CI 68·9 to 69·3)mmHg to a minimum of 68·5 (95% CI 68·3 to 68·7)mmHg at 19+5 weeks’ gestation, a change of -0·6 (95% CI-0·8 to -0·4)mmHg. Diastolic blood pressure subsequently increased to a maximum of 76·3 (95% CI 75·9 to 76·8)mmHg at 40 weeks’ gestation. Systolic blood pressure fell by >14 mmHg or diastolic blood pressure by >11 mmHg in fewer than 10% of women at any gestational age. Fewer than 10% of women increased their systolic blood pressure by >24 mmHg or diastolic blood pressure by >18 mmHg at any gestational age. The study’s main limitations were the unavailability of pre-pregnancy blood pressure values and inability to explore circadian effects because time of day was not recorded for the blood pressure measurements. Conclusion Our findings provide international, gestational age-specific centiles and limits of acceptable change to facilitate earlier recognition of deteriorating health in pregnant women. These centiles challenge the idea of a clinically significant mid-pregnancy drop in blood pressure.