Second Trimester Ambulatory Blood Pressure Monitoring Is the Most Predictive Timing for a Composite Adverse Pregnancy Outcome

Objective: To identify the pregnancy trimester in which ambulatory blood pressure monitoring provides the strongest prediction of a composite adverse pregnancy outcome. Design and method: Ambulatory blood pressure monitoring was performed on 329 pregnant women (mean age 32.6 ± 5.6 years; mean body mass index 30.0 ± 6.8 kg/m2). Maternal death, fetal or neonatal death, preeclampsia or eclampsia, gestational diabetes, prematurity, fetal growth restriction, or dystocia brought on by uncontrolled hypertension were the main composite outcomes. Days were used to measure the follow-up period between blood pressure monitoring and the first event. After controlling for age, body mass index, and gestational age at monitoring, Cox proportional hazards models were fitted independently by trimester at monitoring (first trimester up to 13 weeks; second trimester 14–27 weeks; third trimester 28 weeks or more). Kaplan-Meier curves used the log-rank test to compare time to event between trimesters. Results: 47 women had ambulatory blood pressure monitoring during the first trimester, 167 during the second, and 99 during the third. Time to the composite outcome varied significantly between trimesters (log-rank p=0.023), according to Kaplan–Meier analysis. There were significant pairwise differences between the first and second trimesters (p=0.018) and the first and third trimesters (p=0.037), but not between the second and third trimesters (p=0.779). The second trimester had the best prognostic performance in trimester-stratified Cox models. With a borderline association for daytime systolic blood pressure (hazard ratio 1.021; p=0.051), the composite outcome was predicted by 24-hour systolic blood pressure (hazard ratio 1.024 per 1 millimeter of mercury; p=0.032), nighttime systolic blood pressure (hazard ratio 1.022; p=0.046), and both. Neither the first trimester (all p>0.333) nor the third trimester (all p>0.108) showed any significant associations. Across trimesters, diastolic blood pressure parameters did not attain statistical significance. Conclusions: Systolic ambulatory blood pressure provides the most reliable prognostic information, and the second trimester seems to be the most predictive time for ambulatory blood pressure monitoring to identify pregnant women at increased risk of a composite adverse pregnancy outcome.