(143) Normal Blood Pressure Standard Across Gestation in Low-Risk Pregnant Individuals and Comparisons by Pregnancy Outcome

Objective:
Nearly 50 years ago, mean blood pressure (BP) in 6,662 white pregnant women was reported to vary by gestational age, but the upper and lower limits of normal across gestation have not been defined. Our objectives were to create a BP standard based on the gestational age-specific BP in low-risk pregnant people, and to compare BP trajectories between those with and without hypertensive disorders of pregnancy (HDP; gestational hypertension or preeclampsia), spontaneous preterm delivery (sPTD), or small-for-gestational age neonates (SGA).

Study Design:
This was a secondary analysis of 2334 low-risk, singleton pregnancies from 2009-2013 that were a part of a prospective NICHD cohort of individuals 18-40 years without medical conditions or prior pregnancy complications; BMI 19.0-29.9 kg/m2. Linear mixed models with cubic splines were used to estimate systolic and diastolic BP curves, based on BP abstracted from prenatal records. Likelihood ratio tests compared curves between pregnancies with HDP, sPTD, or SGA (< 10%ile based on Duryea reference) vs. those without these outcomes, adjusting for confounders.

Results:

There were 2278 pregnancies included in the standard with a mean of 11 measurements (standard deviation [SD] 3). The mean maternal age was 28.2y (SD 5.5), gestational age at delivery 38.8wk (SD 1.7), and 49% were nulliparous. Participants were 28% Hispanic, 26% non-Hispanic (NH) Black, 26% NH white, and 20% NH Asian. HDP occurred in 123 (6%), sPTD in 90 (4%), and SGA in 191 (9%). BPs were lower and varied less with gestation than reported in the prior study, with standard curves shown in Figure 1. As early as at 6-8 weeks, BPs were significantly higher in those who ultimately developed HDP and sPTB compared to those who did not (p values < 0.05, Figure 2).



Conclusion:
In a diverse, contemporary cohort, we established normative BP curves and trends for pregnancy. Additionally, early first-trimester BPs are higher for those destined to have HDP or sPTB. Future studies should evaluate whether deviation of BP trajectories is an opportunity for early intervention to decrease risks of HDP and sPTB.