Hypertensive disorders of pregnancy: Clinical practice

Hypertensive disorders of pregnancy are diseases that cause high blood pressure during pregnancy - either a systolic blood pressure higher than 140 mmHg, or a diastolic blood pressure higher than 90 mmHg, or both. To make the diagnosis, two separate blood pressure measurements taken at least 4 hours apart have to be elevated.

Hypertensive disorders of pregnancy are organized by their time of onset and the presence of proteinuria.

Before 20 weeks gestation, chronic hypertension is usually the cause of hypertension, and there isn’t usually proteinuria.

Chronic hypertension in pregnancy requires antihypertensive medication when systolic blood pressure is over 160 mmHg, or when diastolic blood pressure is over 110 mmHg, and options include labetalol, nifedipine or methyldopa, with a goal to get blood pressure below 150 over 100 mmHg.

Delivery is recommended between 38 and 40 weeks of gestation in females not requiring medication; between 37 and 40 weeks for females with hypertension controlled with medication, and between 36 and 38 weeks for females with severe and difficult to control hypertension.

After 20 weeks gestation, the possible causes are gestational hypertension, which doesn’t cause proteinuria, and preeclampsia and eclampsia, both of which do cause proteinuria.

Gestational hypertension is relatively benign, but many females with gestational hypertension progress to developing preeclampsia.

Females with non-severe gestational hypertension, meaning less than 160 over 110 mmHg, can be managed as outpatients, with weekly or twice weekly follow-up visits to measure blood pressure and protein excretion.

Females are instructed to monitor their blood pressure and fetal kick count daily, and at each visit starting at 32 weeks of gestation, a fetal ultrasound, a non-stress test or NST should be done, and sometimes a biophysical profile is indicated.

On an ultrasound, fetal growth and the amount of amniotic fluid can be estimated.

An NST is a 20 minute recording of fetal heart rate using a cardiotocograph - also called an electronic fetal monitor.

On a normal NST, fetal heart rate varies between 110 and 160 beats per minute, and has at least 2 accelerations - defined as increases of 15 beats per minute in fetal heart rate, lasting for more than 15 seconds in pregnancies beyond 32 weeks, or 10 beats per minute lasting for at least 10 seconds in pregnancies below 32 weeks.

A lower heart rate, fewer or shorter accelerations mean the NST is non-reactive, and warrants a biophysical profile, or a BPP.

A biophysical profile is an evaluation of the fetus that is scored based on 5 criteria.

The first criterion is the NST result.

The other four are fetal breathing movements, fetal torso and limb movements; muscle tone, and the amount of amniotic fluid, and all four of these are evaluated on an ultrasound.

2 points are awarded for each of the five criteria, adding up to a maximum of 10 points, and the higher the score, the better - and 6 out of 10 or above is considered a good score, which signifies the fetus is generally doing well.

If a female has non-severe gestational hypertension that doesn’t progress to preeclampsia and the fetus is healthy, then the delivery can be done at term.

If the female has severe gestational hypertension, then antihypertensive medication like labetalol, nifedipine or methyldopa are given with a goal of lowering blood pressure to below 150 over 100 mmHg.

Delivery depends on gestational age at diagnosis - for pregnancies 34 weeks or further along, delivery is recommended.

For pregnancies less than 34 weeks along, the female should be hospitalized, with frequent monitoring.

Additionally, a course of antenatal corticosteroids is recommended to help the fetal lungs mature faster - most frequently, two doses of 12 milligrams of betamethasone are given intramuscularly 24 hours apart.

If blood pressure is easily controlled with medication, the fetus is healthy, and preeclampsia doesn’t develop, then the delivery can be done between 34 and 36 weeks of gestation.

After delivery, gestational hypertension usually returns back to normal within 12 weeks.

Now, if a female does have proteinuria, then she has preeclampsia, and if that female develops seizures, then it’s called eclampsia.

The gold standard for measuring urine protein levels is a 24 hour urine protein level - and proteinuria is defined as more than 300 milligrams of protein excreted in a day.

An acceptable alternative is to determine the urine protein to creatinine ratio using a random urine sample, and there is proteinuria when the ratio is greater than 0.3 milligrams of protein per milligram of creatinine.

The least preferred option is a urine dipstick test - with anything above 1+ suggesting proteinuria.

However, both a positive and negative urine dipstick test has to be confirmed with a 24-hour urine protein level.

Now although preeclampsia is defined as hypertension and proteinuria after 20 weeks of pregnancy, in some cases it may develop up to 6 weeks after delivery.

Additionally, females with chronic hypertension are much more likely to develop preeclampsia.

Preeclampsia also tends to occur more often during a first pregnancy, in pregnancies with more than one baby, or in mothers 35 years or older.

Other risk factors include diabetes, lupus, obesity, and a family history of preeclampsia.