Introduction

Gestational hypertension is a major concern as people move through their pregnancy.  Abnormal blood pressures indicating a hypertensive disorder is a significant cause of adverse maternal and neonatal outcomes worldwide.  Preeclampsia along with infection and hemorrhage are the three largest cases of maternal mortality currently.  It is thought that 1 in 4 deaths that occur from hypertension/preeclampsia in pregnant people are preventable. A new study was just released “A new definition of gestational hypertension? New-onset blood pressures of 130 to 139/80 to 89 mm Hg after 20 weeks of gestation” that attempts to predict those pregnant people who may be at risk of experiencing a hypertensive disorder of pregnancy.

In 2017, the American Heart Association (AHA) and the American College of Cardiology (ACC) released new blood pressure guidelines that lowered the diagnostic threshold for hypertension.  Previously the criteria was a reading equal to or greater than 140/90, (now defined as stage 2 hypertension) but now a reading in the range of 130/80 to 139/89 (now defined as stage 1 hypertension) is considered hypertensive and should initiate further monitoring and treatment.

Researchers wanted to examine whether documented blood pressures at 20 weeks gestation or beyond that fell into the stage 1 hypertensive range put the pregnant person at higher risk of adverse pregnancy outcomes.

How the study was done

Information for this retrospective study was collected at Barnes-Jewish Hospital in St. Louis, MO between January 01, 2014 and June 08, 2016 from people pregnant with a singleton who received prenatal care and delivered at that facility during that time.  Research clinicians extracted blood pressure information, demographic details, and delivery outcomes from the medical records.  To be included in the data pool, patients had to have had at least one prenatal visit prior to 20 weeks, had regular blood pressure checks after 20 weeks and delivered at or after 23 weeks of gestation.

Patients were excluded for multiple gestations, pre-existing diagnosis of hypertension before 20 weeks of gestation or if they did not ultimately deliver at Barnes-Jewish.

Qualified subjects were then sorted into two groups: Normotensive patients who had all blood pressure readings below 130/80 before 20 weeks of gestational age  and no pre-existing conditions of chronic hypertension and the exposure group, consisting of people who had a single maximum blood pressure reading of 130 to 139/80 to 89 between 20 gestational weeks and birth.  The control group consisted of people who did not have any readings over 130/80 between 20 weeks and delivery.

The primary outcome measured was the development of any hypertensive disorder of pregnancy (HDP) which might include gestational hypertension, preeclampsia (and assorted symptoms)  or eclampsia at the time of admission or delivery.  The researchers also looked  at those patients who were readmitted for any of these conditions along with secondary outcomes in the birthing person or in the newborn, including hemorrhage, ICU admit, NICU admit, heart failure, intubation, pulmonary edema, kidney injury, small for gestational age newborns, preterm births, intrauterine death, APGAR scores less than 3 at 5 minute, low umbilical artery pH, respiratory support needs, neonatal seizures or neonatal death prior to discharge.

What were the results

2090 normotensive people qualified to be included in the project.  63% of these patients remained normotensive until delivery admission and 37% were classified as stage 1 hypertensive as a result of blood pressure elevations between 130 and 139/80 to 89 in the period of 20 weeks and delivery admission.  Researchers share the differences observed in regards to race, parity, gestational age and delivery, average maximum blood pressure, BMI, rates of pregestational and gestational diabetes and birthweight in the table below.

The birthing people with a maximum blood pressure of 130 to 139/80-89 after 20 weeks of gestation were more likely to be multips, obese and have higher rates of pregestational and gestational diabetes.  Those patients identified as stage 1 hypertensive (a maximum blood pressure of 130 to 139/80-89 after 20 weeks of gestation) were 2.4 times more likely to experience a hypertensive disorder of pregnancy and almost 3 times more likely to experience preeclampsia compared with the people who did not have blood pressure readings in those ranges.  Other observations included more small for gestational age babies, patients readmitted to the hospital for postpartum hypertensive disorders of pregnancy,  and more babies to the NICU but these factors did not reach statistical differences.  The two groups did not differ in terms of other pregnancy outcomes.

Discussion

When applying the new AHA and AAC definitions of hypertensive disorders, breaking them in to stage 1 (130-139/80-89) and stage 2 (140/90), those people who fall into stage 1 after 20 weeks of gestation were identified as at increased risk for developing a hypertensive disorder of pregnancy at delivery admission.  More modest blood pressure readings may be an indicator of  HDP disease.  Researchers suggest that providers may want to consider elective induction at 39 weeks to reduce the risk of developing a full blown HDP further in the pregnancy before delivery.  About 25% of people with blood pressure elevation of 130 to 139/80 to 89 mm Hg ultimately developed an HDP as currently defined at or after 39 weeks of gestation, whereas only 7.9% of normotensive people did.

Researchers acknowledge that a randomized control trial should be conducted to determine what the benefits might be for an earlier delivery and whether interventions are warranted.   They also state that people with blood pressure readings below the stage 1 thresholds are likely to remain normotensive but those who fall in the stage 1 level may benefit from increased observation throughout the rest of pregnancy.

Some limitations of the study

The study was retrospective and the method for blood pressure determination was not standardized.  Participants were sorted into the different cohorts based on one reading obtained after 20 weeks gestation.  Current acceptable diagnostic criteria is two abnormal readings.

Conclusion

According to the the researchers: “This study reported that normotensive women with newly elevated blood pressures between 130 and 139/80 and 89 mm Hg after 20 weeks of gestation are almost 3 times as likely to develop HDPs and preeclampsia with severe features at or during their delivery hospitalization. Furthermore, a larger proportion of these women receive a diagnosis during the postpartum period. Further investigation is needed to identify the optimal threshold for diagnosis of HDPs and timing of delivery considerations in this population to reduce maternal morbidity.”

Takeaway for childbirth educators

When discussing gestational hypertension and preeclampsia with families during classes, informing them of these new considerations (and ranges) of who might be at risk of developing a hypertensive disorder of pregnancy can be shared.  Helping them to be aware and discuss the blood pressure readings that are observed at their prenatal  appointments with their providers to determine the best  plan of care to keep them in the normotensive range and free from possible interventions that may occur as they approach full term.

References

Porcelli BA, Diveley E, Meyenburg K, et al. A new definition of gestational hypertension? New- onset blood pressures of 130 to 139/80 to 89 mm Hg after 20 weeks of gestation. Am J Obstet Gynecol 2020;223:442.e1-7.

Published: September 10, 2020

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