Hypertension in Pregnancy (ACOG)

About Hypertension in Pregnancy (ACOG)

Hypertensive disorders of pregnancy are among the leading causes of maternal and fetal morbidity and mortality worldwide. The American College of Obstetricians and Gynecologists (ACOG) published its most recent comprehensive practice bulletin on hypertension in pregnancy in 2020 (reaffirmed 2022), which standardized the definitions of gestational hypertension, preeclampsia, preeclampsia with severe features, and chronic hypertension with superimposed preeclampsia. The classifications are clinically important because they drive decisions about fetal monitoring, antihypertensive therapy, magnesium sulfate for seizure prophylaxis, and the timing of delivery.

What the calculator measures

The calculator classifies a pregnant woman's blood pressure and other clinical findings into one of five diagnostic categories. The output is a diagnostic label that drives clinical management decisions. The categories reflect the ACOG 2020 criteria:

• Normotensive: BP <140/<90 mmHg after 20 weeks' gestation (and no prior hypertension).
• Gestational hypertension: BP ≥140/90 mmHg on two occasions at least 4 hours apart after 20 weeks' gestation, in a previously normotensive woman, without proteinuria or severe features.
• Preeclampsia (without severe features): BP ≥140/90 mmHg plus proteinuria (≥300 mg/24h or P/C ratio ≥0.3 or dipstick ≥1+) OR BP ≥140/90 mmHg plus thrombocytopenia, renal insufficiency, impaired liver function, pulmonary edema, or cerebral/visual symptoms.
• Preeclampsia with severe features: BP ≥160/110 mmHg on two occasions at least 4 hours apart (unless antihypertensive therapy is started before this time), OR platelet count <100,000/μL, OR serum creatinine >1.1 mg/dL or doubling of baseline, OR transaminases ≥2x normal, OR pulmonary edema, OR new-onset headache unresponsive to acetaminophen, OR visual symptoms.
• Chronic hypertension (preexisting): Hypertension present before pregnancy or before 20 weeks' gestation.
• Chronic hypertension with superimposed preeclampsia: Chronic hypertension plus new-onset proteinuria, sudden increase in proteinuria, sudden increase in BP, thrombocytopenia, renal insufficiency, impaired liver function, pulmonary edema, or cerebral/visual symptoms.

How the formula works

The calculator applies the ACOG diagnostic algorithm. Hypertension in pregnancy is defined as BP ≥140 mmHg systolic or ≥90 mmHg diastolic on two occasions at least 4 hours apart (a single reading is not sufficient for diagnosis). Severe hypertension is BP ≥160 mmHg systolic or ≥110 mmHg diastolic, which requires more urgent confirmation (within minutes, not 4 hours). Proteinuria is defined as ≥300 mg in a 24-hour urine collection, or a protein/creatinine ratio ≥0.3 mg/mg, or a dipstick ≥1+ if quantitative methods are not available. The calculator also asks about 'severe features', a binary input that captures any of the following: severe-range BP (≥160/110), thrombocytopenia (platelets <100,000), elevated creatinine (>1.1 mg/dL or doubling of baseline), elevated transaminases (≥2x upper limit of normal), pulmonary edema, or new-onset headache unresponsive to acetaminophen or visual symptoms. The presence of any severe feature changes the diagnosis from 'preeclampsia without severe features' to 'preeclampsia with severe features' and triggers more aggressive management (magnesium sulfate for seizure prophylaxis, delivery at 34 weeks if unstable, expectant management only in select cases).

Interpretation

The diagnosis drives the following management decisions (per ACOG 2020):

• Gestational hypertension without severe features: Weekly to twice-weekly BP monitoring, fetal monitoring (weekly nonstress test from 32 weeks), and antihypertensive therapy if BP ≥160/110. Delivery at 37 weeks.
• Preeclampsia without severe features: Same as gestational hypertension, with the addition of maternal laboratory monitoring (CBC, LFTs, creatinine). Delivery at 37 weeks.
• Preeclampsia with severe features: Magnesium sulfate for seizure prophylaxis, antihypertensive therapy (target BP <160/110), and delivery at 34 weeks (or earlier if maternal or fetal deterioration). Expectant management before 34 weeks may be considered in a tertiary care center.
• Chronic hypertension: Lifestyle modification (low-sodium diet, exercise), antihypertensive therapy if BP ≥160/110 (methyldopa, labetalol, or nifedipine are preferred; ACE inhibitors and ARBs are contraindicated). Delivery at 37-39 weeks.
• Chronic hypertension with superimposed preeclampsia: Management as for preeclampsia with or without severe features.

Clinical use

The calculator is most useful at the point of care, when a pregnant woman's blood pressure and other clinical findings are being interpreted. The classification drives the urgency of follow-up, the decision to initiate antihypertensive therapy, the decision to initiate magnesium sulfate for seizure prophylaxis, and the timing of delivery. The ACOG criteria are the standard for U.S. practice; international criteria (e.g. the NICE guideline in the UK, the ISSHP criteria) are similar but not identical.

Limitations

The calculator has several limitations. First, it uses a single BP reading; the diagnosis of hypertension in pregnancy requires confirmation with a second reading at least 4 hours apart (or within minutes for severe-range BP). Second, the calculator's 'severe features' input is binary and does not capture the specific severe feature (e.g. thrombocytopenia vs. visual symptoms), which has different prognostic implications. Third, the calculator does not capture the rate of BP change, which is an important prognostic factor. Fourth, the calculator does not capture fetal status (growth restriction, abnormal Doppler, oligohydramnios), which influences the timing of delivery. Fifth, the calculator should not be used in isolation, the diagnosis and management of hypertensive disorders of pregnancy require integration of maternal and fetal status, gestational age, and the patient's preferences and values.

Comparison with non-pregnant BP criteria

The ACOG criteria for hypertension in pregnancy (≥140/90 mmHg) are more conservative than the 2017 ACC/AHA criteria for non-pregnant adults (≥130/80 mmHg). This conservative threshold reflects the unique physiology of pregnancy (in which BP normally decreases in the second trimester and rises in the third) and the higher stakes of maternal and fetal complications. The 2017 ACC/AHA criteria do not apply to pregnant women, who should be managed according to the ACOG criteria.

How to use the result

A pregnant woman at 32 weeks' gestation with BP 142/94 mmHg and a P/C ratio of 0.4 mg/mg has preeclampsia without severe features. Management includes weekly maternal and fetal monitoring, laboratory monitoring (CBC, LFTs, creatinine), antihypertensive therapy if BP ≥160/110, and delivery planning at 37 weeks. The patient should be educated about warning signs (severe headache, vision changes, right upper quadrant pain, shortness of breath) and instructed to seek immediate care if these develop.