International gestational age-specific centiles for blood pressure in pregnancy from the INTERGROWTH-21st Project in 8 countries: A longitudinal cohort study

Author summary Why was this study done? Internationally applicable gestational age-specific centiles for blood pressure are needed in clinical practice to determine when women have left the normal range. It is uncertain whether clinically significant decreases in blood pressure occur between early and midpregnancy. What did the researchers do and find? We estimated international gestational age-specific blood pressure centiles using longitudinal blood pressure data provided by women from 8 countries who took part in the International Fetal and Newborn Growth Consortium for the 21st Century (INTERGROWTH-21st) Project. On average, systolic blood pressure rose by around 8 mmHg between 12 and 40 weeks' gestation, with no decrease in midpregnancy. Diastolic blood pressure decreased slightly (by around 0.6 mmHg) between 12 and 19 weeks, rising thereafter until 40 weeks' gestation. At any gestational age, systolic blood pressure fell by >14 mmHg and diastolic blood pressure by >11 mmHg from baseline in fewer than 10% of women. Fewer than 10% of women increased their systolic blood pressure by >24 mmHg or diastolic blood pressure by >18 mmHg at any gestational age. What do these findings mean? Our findings challenge the frequently quoted midpregnancy blood pressure decrease, advocating for a higher index of clinical suspicion when a woman presents with a lower than booking blood pressure, especially in late pregnancy. We show the limits for acceptable change in blood pressure during healthy pregnancy, which should help clinicians determine patients with abnormal blood pressure rises and falls. 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 International Fetal and Newborn Growth Consortium for the 21st Century (INTERGROWTH-21st) Fetal Growth Longitudinal Study (FGLS) to produce international, gestational age-specific, smoothed centiles (third, 10th, 50th, 90th, and 97th) for blood pressure. Methods and findings Secondary analysis of a prospective, longitudinal, observational cohort study (2009 to 2016) was conducted across 8 diverse urban areas in Brazil, China, India, Italy, Kenya, Oman, the United Kingdom, and the United States of America. We enrolled healthy women at low risk of pregnancy complications. We measured blood pressure using standardised methodology and validated equipment at enrolment at <14 weeks, then every 5 +/- 1 weeks until delivery. We enrolled 4,607 (35%) women of 13,108 screened. The mean maternal age was 28 center dot 4 (standard deviation [SD] 3.9) years; 97% (4,204/4,321) of women were married or living with a partner, and 68% (2,955/4,321) were nulliparous. Their mean body mass index (BMI) was 23.3 (SD 3.0) kg/m(2). Systolic blood pressure was lowest at 12 weeks: Median was 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 center dot 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 prepregnancy blood pressure values and inability to explore circadian effects because time of day was not recorded for the blood pressure measurements. Conclusions 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 midpregnancy drop in blood pressure.

Automated summary

This study estimated gestational age-specific blood pressure centiles and found that systolic blood pressure increased gradually while diastolic blood pressure decreased slightly in midpregnancy before rising again. The results challenge the concept of a significant midpregnancy drop in blood pressure, advocating for increased vigilance towards blood pressure decreases.