Hypertension in Pregnancy

December 14, 2007

Chronic hypertension and Gestational Hypertension

A rose by any other name...

Historically, it didn't take long for folks to realize that there were certain conditions unique to pregnancy. What got their attention was death, which seemed to be an accepted hazard of trying to reproduce. There were two main mortal conditions associated with childbirth-related death. One was hemorrhage. The other was something that was called toxemia, described as far back as four thousand years ago.

Toxemia, so called because it was supposed that toxins of some sort, bad "humors," caused this condition, was associated with seizures, swelling, and death anywere from the beginning of the third trimester to a month or so beyond delivery. As science gloated over discoveries like blood types and blood pressure differences, the voodoo term "toxemia" was renamed "pre-eclampsia", "eclapmsia" a condition of seizures that were the result of the worst type of swelling one could have--brain swelling. But "pre-"eclampsia was a bit of a downer term, because implied within it was the observation, "You haven't had your seizure...yet!"

Next, the label was corrected to "Pregnancny-Induced Hypertension" ("PIH"), to associate it with the uniqueness of pregnancy. But this term singled out only one aspect, the elevated blood pressure. This was a faulty term, because it was possible to have PIH and its sinister big sister, HELLP syndrome, without even having an elevation in blood pressure. Today, the term du jour is Gestational Hypertension...still not perfect, but we all know what we're talking about here: a multifactorial condition, involving some sort of immune response to pregnancy. After all, there's foreign material (the father's genetic component) trying to graft to the mother, with varying intensities of rejection. These "varying intensities" probably are responsible for the numerous ways it presents in different pregnant women, which has been the difficulty in nailing down one "Grand Unification Theory" of its cause. In fact, there's an empty plaque at Chicago's famous Lying-in Hospital waiting for the engraved name of the person who discoveres the cause. This plaque may remain empty forever, as the "cause" may run the gamut of immunology, host-graft science, embryology, perinatology, chemistry, biochemistry, molecular biology, and a host of other biological and physical sciences.* There may be thousands of researchers that would have be included on a very, very large plaque.

Chronic hypertension and gestational hypertension during pregnancy are really two different conditions.

There are three distinct types of high blood pressure that can complicate pregnancy. One type, not pregnancy-related, is called chronic hypertension, and is has minimal impact on a pregnancy if well controlled. The other is called Pregnancy-Induced Hypertension (PIH) and can be devastating. (The third type is merely a combination of the two.)

Pregnancy complicated by chronic hypertension

Chronic hypertension is high blood pressure, usually greater than 140/90. High blood pressure is famous for banging up blood vessels and the organs supplied by them. The hypertensive patient, feeling fine for years, may ultimately see this damage as strokes in the brain, heart disease and heart attacks in the heart, and kidney damage.

Strokes and heart attacks are serious enough, but damage to the kidney could further encourage more hypertension because the kidneys play an important role in managing normal blood pressure in healthy people.

Substances called angiotensins are part of a cascade of chemistry in the kidneys, and they are important in raising blood pressure, ordinarily to maintain normal levels in healthy conditions. So it is not surprising that one of the newer drug types to treat hypertension is a medicine that blocks the chemical reactions that the angiotensins take part in. They are called ACE inhibitors ("Angiotensin-1 Converting Enzyme" inhibitors), and they include catopril, micardis, and the brand name Vasotec (enatapril).

But these popular medications are suspected of causing deformities to babies, specifically if given in the later trimesters, so pregnant patients with high blood pressure are left with the older treatments. Fortunately, there are a lot of them, and they still all work pretty well.

For example, Lopressor (metoprolol) and labetalol act by blocking the nerves that constrict the muscles in arteries and strengthen the heart's contraction efforts (= lower blood pressure). Aldomet (methyldopa) works in a similar way, but is less selective in the particular nerve effects, meaning there may be more side effects.

Untreated, hypertension can also affect the baby as well as the mother. The same damaging effects to the blood vessels in the expectant mother can also damage the blood supply involved with placental exchange of oxygen and nutrition from mother to baby. This can age the placenta prematurely, and the famous result in hypertensive pregnancies is intrauterine growth restriction (IUGR--small babies) and oligohydramnios (low amount of amniotic fluid). Ironically, hypertension in the mother so blocks the normal nutritional exchange that the fetus has the opposite problem--hypotension (low blood pressure)--which can endanger the fetal kidneys, decreasing the amount of urine the unborn baby produces (the urine being the most significant portion of amniotic fluid).

ACE inhibitors will exaggerate this danger considerably, so it is recommended that ACE inhibitors be discontinued as soon as pregnancy is diagnosed. One relief to the newly pregnant patients who have been on ACE inhibitors is that the danger seems to be in the later point of pregnancy, so getting off of them in early pregnancy is probably all that need be done to relieve any worries.

(The American College of Obstetricians and Gynecologists states, "With the exception of the ACE inhibitors, there is no need to discontinue any of the other drugs commonly used to treat hypertension in a pregnant patient whose blood pressure is well controlled.")

The plot thickens...Gestational Hypertension

A particular condition of pregnancy--a complication--is now called Gestational Hypertension (previously, pregnancy-induced hypertension (PIH), pre-eclampsia, and toxemia) which is quite different from the "chronic" hypertension discussed. Although the exact cause of it is unknown, it seems to be an immunologic rejection of the pregnancy, the baby seen as a hostile tissue-graft reaction. This is a much more dangerous condition than chronic hypertension, because there is much more alteration in the maternal body than just high blood pressure. There's a whole chemical shift of maladaptative reactions that can even lead to seizures and death in the pregnant patient.

Brain swelling is the cause of seizures, lethargy, and visual disturbances. (The visual disturbances are not to be confused with the swelling of your cornea which results in blurred vision, which reverses after birth and is harmless.) The expectant mother's kidneys are especially vulnerable, affecting filtration, worsening the swelling and resulting in the loss of protein in the urine. The blood vessels develop abnormalities of constriction, affecting blood pressure, and the reflexes become hyperactive

The blood pressure changes are only part of the "classical tetrad" of signs. These four noteworthy signs and symptoms are:

  • High blood pressure,
  • Edema (swelling, more suggestive of gestational hypertension if it is central of the face rather than peripheral of the ankles--peripheral swelling is normal),
  • Hyperproteinurea, or spilling protein in the urine, and
  • Hyper-reflexia, or exaggerated deep tendon reflexes (the knee-jerk, for instance).

While chronic hypertension, on the one hand and even in pregnancy, is a slow-growing problem that allows plenty of time for managementgeek that seldom interferes with bringing a pregnancy to term, gestational hypertension can progress swiftly to prompt delivery prematurely.

The most severe form of gestational hypertension, HELLP Syndrome, is a true obstetrical emergency, affecting blood clotting abilities and liver function.

Chronic hypertension is the tortoise...

PIH is the hare.

In this race there are no real winners, but as an obstetrician, I'd much rather go with the tortoise.

The worst case scenario is the pregnant patient with pre-existing hypertension who develops a gestational hypertension overlay.

So in pregnancy there are actually three conditions that involve hypertension:

  • CHRONIC HYPERTENSION (the most manageable of the three, as discussed above),
  • GESTATIONAL HYPERTENSION (PIH, pre-eclampsia, or "toxemia"), which is much more dangerous, and
  • COMBINED: chronic hypertension + gestational hypertension (the worst possibility)

Telling the difference between chronic hypertension and gestational hypertension

One of the perplexing challenges for an obstetrician is to tell the difference between chronic hypertension and PIH when a patient presents with hypertension.

First of all, just what is a normal blood pressure?

I've always told my patients that the best blood pressure is the lowest one you can have without passing out. In the non-pregnant state we doctors like to see the blood pressures be under 140/90. Lately the internal medicine specialty has labeled a "gray zone" of what is called "pre-" hypertension, that zone from 120/80 to 140/90. This is a zone where most agree trouble is brewing, raising the risk of hypertension as disease in the future.

In pregnancy, blood pressures tend to be a little lower, anywhere from 90's/50's to 110's/70's.

A patient with chronic hypertension will generally begin her pregnancy with hypertension or come to me on anti-hypertensive medication from another doctor (a sure tip-off!). Unless there are major changes during the pregnancy (like piling on PIH, too), the blood pressure of a chronic hypertensive patient will usually behave itself, rising only slightly over the course of the pregnancy.

On the other hand, a patient that develops PIH will begin her pregnancy with a normal blood pressure, but it will rise sometime in the third trimester in typical cases, earlier in severe cases. The actual criteria that need to be met before suspecting PIH is a rise in the systolic number (the top number) of 30 and/or a rise of the diastolic number (the bottom number) of 15. For example, a blood pressure that usually runs about 100/60 and then presents as 140/84 would warrant suspicion.

The cure for gestational hypertension is delivery. Back in the days when we called it "pre-"eclampsia, what we really feared was "eclampsia." Before the modern protocols of prenatal care were introduced, women would often show up at the hospital either having seizures or having had one. Since the seizures were from brain-swelling, eclampsia could kill or cause brain damage. So when a patient is being followed in her pregnancy for gestational hypertension, this is a high-risk situation that commands close attention--often hospitalization.

The trick is to get a baby to maturity before having to "unload" because of this complication. See Management below.

Diagnosing the severity of gestational hypertension

Still one of the most sensitive tests for how severe it is involves collecting a 24-hour urine for protein. With the "hyperproteinurea," the amount of protein spilled in the urine increases due to the changes in the kidneys that are a result of the disease. The amount of protein can be measured and certain thresholds used to determine severity of illness. (Chronic hypertension doesn't usually involve spilling protein in the urine, and the 24-hour urine can be used to separate the two types of hypertension.)

The amount of hyper-reflexia--just how jumpy the knee-jerk reflex is--is a rather subjective way to add to the alarm in severe gestational hypertension. Swelling is probably the least reliable, but when central swelling of the face shows up, there are usually enough of the other things happening to make this an incidental finding.

As mentioned above, a rise in the blood pressure by 30/15 (for example, 90/50 ---> 120/70) over the course of the pregnancy is a diagnostic criterium, even though the final pressures may seem normal from what's normal in the general population. This is why prenatal care is so important. It's not unheard of for a woman to present for the first time in late pregnancy with what seemed like a normal pressure (and nothing prior to compare it to) who would then surprise everyone with a seizure.

Management of gestational hypertension

If a patient has only mild disease, this can be followed conservatively, but there are those who will argue that there is no such thing as "mild" gestational hypertension and advise delivery as soon as the baby is deemed lung-mature. Bed rest, a low salt diet, and peace and quiet are the treatment before delivery, and this regimen hasn't changed in over a hundred years. Of course close observation with frequent blood pressures, serial 24-hour urine collections, and liver and coagulation studies go with this conservative treatment. That's how we watch the mother. We do non-stress tests and biophysical profiles to watch the baby. As soon as the patient's cervix is inducible near term, induction for delivery is recommended.

If a patient has severe disease, delivery will be indicated regardless of the gestational age, possibly creating peril for the baby if it's too early. And in cases that are of intermediate severity, the judgement of the obstetrician and how fast the situation is deteriorating will determine the decision that is individualized for the patient's unique situation. Sometimes in an "iffy" transition period from prematurity to maturity, an amniocentesis can prove or disprove lung maturity, prompting delivery or championing waiting as long as the gestational hypertension is stable.

Magnesium sulfate is a muscle-relaxer that is used to compete with calcium, decreasing the risk of seizure. The amount used is increased until the knee-jerk reflex is just about absent (but it's really adjusted based on blood levels). It is a safe medicine but needs careful monitoring--levels too high will cause respiratory depression. It also is useful in stopping premature labor. Lately it has been implicated in possilby affecting the unborn baby unfavorably, but this risk is far outweighed by the benefit because of what we're dealing with here.

The longer a patient is pregnant, the more severe the disease can become. This is not so much a matter of how long the patient has been pregnant, but how pregnant she is. What I'm getting at is that twins and triplets can cause PIH sooner than usual, and the severity can increase faster than usual. These are already high-risk conditions for premature delivery, so adding the complication of PIH makes a multiple gestation even more dangerous.

Gestational Hypertension Can Get Worse

There are some particularly sinister forms of gestational hypertension. Thrombocytopenia (low platelet count) can appear as a sole problem. Since platelets are part of the blood-clotting system, hemorrhage and strokes can occur if the platelet count gets low enough. HELLP syndrome (low platelets associated with liver disease) is an obstetrical emergency and requires prompt delivery.

Treatment with anti-hypertensives in gestational hypertension is useful in lowering the blood pressure, but merely making the blood pressure go down won't stop the disease. The damage and danger will still rage in the background.

 

In gestational hypertension, the high blood pressure is not the disease, but an effect of the disease. (In chronic hypertension, for the most part, high blood pressure really is the disease

True, pregnancy and delivery are natural events. But things like chronic hypertension and gestational hypertension are what prenatal care is all about. Watchful waiting is better than just waiting.

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