What is an optimal BP target when treating chronic hypertension in pregnancy?
When treating chronic hypertension in pregnant patients, a concern is that reducing maternal BP may decrease uteroplacental perfusion and result in fetal growth restriction. However, a recent trial reported that a BP treatment target < 140/90 mm Hg is associated with better outcomes for both mother and newborn than withholding antihypertension medications. In the trial, 2,408 women with chronic hypertension diagnosed before 20 weeks of gestation were randomly assigned to an active treatment group with prescription of antihypertension medicines to achieve a BP target of < 140/90 mm Hg; or to a control group where no antihypertension or no additional antihypertension treatment was prescribed unless BP was ≥ 160 mm Hg systolic or ≥ 105 mm Hg diastolic.9 The hypertension medications prescribed to the patients in the active treatment group were labetalol (63.2%), nifedipine (33.4%), amlodipine (1.7%), methyldopa (0.5%), hydrochlorothiazide (0.3%), metoprolol (0.2%), and missing/unknown/other (0.7%).9
If a patient in the control group developed severe hypertension, they were started on an antihypertension medicine and the BP treatment target was < 140/90 mm Hg. Compared with the control regimen, active treatment resulted in a significant decrease in the development of preeclampsia (24.4% vs 31.1%; risk ratio [RR], 0.79; 95% CI, 0.69-0.89), severe hypertension (36.1% vs 44.3%; RR, 0.82; 95% CI, 0.74-0.90), preterm birth < 37 weeks’ gestation (27.5% vs 31.4%; RR, 0.87; 95% CI, 0.77-0.99), preterm birth < 35 weeks’ gestation (12.2% vs 16.7%; odds ratio [OR], 0.69; 95% CI, 0.55-0.88), and low birth-weight (< 2,500 g) newborns (19.2% vs 23.1%; RR, 0.83; 95% CI, 0.71-0.97).9 The percentage of small for gestational age birth weight below the 10th percentile was similar in the treatment and control groups, 11.2% and 10.4%, respectively (adjusted RR, 1.04; 95% CI, 0.82-1.31).9 The number of patients who would need to be treated to prevent one primary-outcome event was 15.9 The investigators concluded that for pregnant patients with chronic hypertension, the optimal BP target is < 140/90 mm Hg.9
When does BP reach a postpartum peak?
In pregnant patients with hypertension, BP may decrease immediately after birth. Following birth, BP tends to increase, reaching a peak 3 to 6 days postpartum.17,18 This pattern was observed in patients with and without preeclampsia in the index pregnancy. Among 136 patients without antepartum preeclampsia, the prevalence of a diastolic BP > 89 mm Hg was 5% and 15% on postpartum days 1 and 3, respectively.17 The postpartum rise in BP may be due to mobilization of water from the extravascular to the intravascular space and excretion of total body sodium that accumulated during pregnancy.19 In one study of 998 consecutive singleton cesarean births, 7.7% of the patients with no recorded elevated BP before delivery developed de novo hypertension postpartum.20 Compared with patients without antepartum or new onset postpartum hypertension, the patients who developed postpartum hypertension had a higher body mass index, were more likely to be Black and to have a history of type 2 diabetes. Compared with patients without antepartum or postpartum hypertension, the patients who developed de novo postpartum hypertension, had significantly elevated soluble fms-like tyrosine kinase-1 and significantly decreased placental growth factor, a pattern seen with preeclampsia.20 These results suggest that de novo postpartum hypertension may have molecular causes similar to preeclampsia.20
Postpartum hypertension should be treated with a medication that is thought to be safe for breastfeeding patients, including labetalol, nifedipine, or enalapril.21-23 The relative infant dose of labetalol, nifedipine, and enalapril is approximately 3.6%, ≤ 3.2%, and 1.1%, respectively.24 If the relative infant dose of a medication is < 10% it is generally considered to be compatible with breastfeeding.25
Many obstetricians have seldom prescribed enalapril, an ACE-I. The initial dose of enalapril is 5 mg or 10 mg daily. After initiation of treatment, the dose can be adjusted based on BP measurement. The maximal daily dose is 40 mg daily in one dose or two divided doses. Similar to other hypertension medicines, enalapril therapy may cause hypotension and dizziness. Enalapril should not be used by pregnant patients because it is associated with an increased risk of congenital anomalies and fetal demise.
Does a HDP increase the risk of developing chronic hypertension?
All obstetricians know that a patient with a history of a HDP is at an increased risk for developing chronic hypertension treated with a medication, but the magnitude of the risk is less well known. In a nationwide study in Denmark, the prevalence of chronic hypertension treated with medication 10 years after delivery among patients with a history of a HDP in their first pregnancy, was 14%, 21%, and 32%, if the first pregnancy occurred in the patient’s 20s, 30s, or 40s, respectively.26 The corresponding prevalence of chronic hypertension in patients without a history of a HDP was 4%, 6%, and 11%, if the first pregnancy occurred in the 20s, 30s, or 40s, respectively.26 Maternal age is an important predictor of who will develop chronic hypertension within 10 years following a pregnancy with a HDP.
In modern obstetric practice, the hypertensive disorders of pregnancy are prevalent and associated with increased maternal and newborn morbidity. Appropriate treatment of hypertension with labetalol, nifedipine, or methyldopa improves maternal and newborn health. Available evidence suggests that maintaining BP < 140/90 mm Hg during pregnancy for most patients is a practical goal with significant benefit. A significant public-health concern is that an increase in the prevalence of HDPs will eventually translate into an increase in chronic hypertension and the attendant complications of heart attack, heart failure, stroke, and renal insufficiency. Recognizing the increased prevalence of HDPs, ObGyns will need to alert patients to their long-term health risks and coordinate appropriate follow-up and treatment to optimize the future health of their patients. ●