Gestational hypertension or pregnancy-induced hypertension (PIH) is the development of new

hypertension Hypertension (HTN or HT), also known as high blood pressure (HBP), is a long-term medical condition in which the blood pressure in the arteries is persistently elevated. High blood pressure usually does not cause symptoms. Long-term high bl ...

in a

pregnant Pregnancy is the time during which one or more offspring develops (gestation, gestates) inside a woman, woman's uterus (womb). A multiple birth, multiple pregnancy involves more than one offspring, such as with twins. Pregnancy usually occur ...

woman after 20 weeks' gestation without the presence of protein in the urine or other signs of

pre-eclampsia Pre-eclampsia is a disorder of pregnancy characterized by the onset of high blood pressure and often a significant amount of protein in the urine. When it arises, the condition begins after 20 weeks of pregnancy. In severe cases of the disease ...

. Gestational hypertension is defined as having a blood pressure greater than 140/90 on two occasions at least 6 hours apart.

Signs and symptoms

No single diagnostic test currently exists to predict the likelihood of developing gestational hypertension. High blood pressure is the major sign in diagnosing gestational hypertension. Some women with gestational hypertension may present asymptomatic, but a number of symptoms are associated with the conditio

Symptoms *

Edema Edema, also spelled oedema, and also known as fluid retention, dropsy, hydropsy and swelling, is the build-up of fluid in the body's Tissue (biology), tissue. Most commonly, the legs or arms are affected. Symptoms may include skin which feels t ...

* Sudden weight gain * Blurred vision or sensitivity to light * Nausea and vomiting * Persistent headaches * Increased blood pressure

Risk factors

Maternal causes *Obesity *Mothers under 20 or over 40 years old *Past history of

diabetes mellitus Diabetes, also known as diabetes mellitus, is a group of metabolic disorders characterized by a high blood sugar level ( hyperglycemia) over a prolonged period of time. Symptoms often include frequent urination, increased thirst and increased ap ...

(particularly gestational hypertension) and

renal disease Kidney disease, or renal disease, technically referred to as nephropathy, is damage to or disease of a kidney. Nephritis is an inflammatory kidney disease and has several types according to the location of the inflammation. Inflammation can b ...

* Pre-existing hypertension *

Thrombophilia Thrombophilia (sometimes called hypercoagulability or a prothrombotic state) is an abnormality of blood coagulation that increases the risk of thrombosis (blood clots in blood vessels). Such abnormalities can be identified in 50% of people who ...

s (anti-phospholipid syndrome, protein C/S deficiency, factor V Leiden) * Having donated a kidney Pregnancy *Multiple gestation (twins or triplets, etc.) *Placental abnormalities: ** Hyperplacentosis: Excessive exposure to chorionic villi ** Placental ischemia Family history * Family history of pre-eclampsia

Diagnosis

Conditions

There exist several hypertensive states of pregnancy: ;Gestational hypertension :Gestational hypertension is usually defined as having a

blood pressure Blood pressure (BP) is the pressure of circulating blood against the walls of blood vessels. Most of this pressure results from the heart pumping blood through the circulatory system. When used without qualification, the term "blood pressure" r ...

higher than 140/90 measured on two separate occasions, more than 6 hours apart, without the presence of protein in the urine and diagnosed after 20 weeks of gestation. ;

Pre-eclampsia Pre-eclampsia is a disorder of pregnancy characterized by the onset of high blood pressure and often a significant amount of protein in the urine. When it arises, the condition begins after 20 weeks of pregnancy. In severe cases of the disease ...

:Pre-eclampsia is gestational hypertension plus

proteinuria Proteinuria is the presence of excess proteins in the urine. In healthy persons, urine contains very little protein; an excess is suggestive of illness. Excess protein in the urine often causes the urine to become foamy (although this symptom ma ...

(>300 mg of protein in a 24-hour urine sample). Severe pre-eclampsia involves a blood pressure greater than 160/110, with additional

medical sign Signs and symptoms are the observed or detectable signs, and experienced symptoms of an illness, injury, or condition. A sign for example may be a higher or lower temperature than normal, raised or lowered blood pressure or an abnormality showin ...

s and

symptom Signs and symptoms are the observed or detectable signs, and experienced symptoms of an illness, injury, or condition. A sign for example may be a higher or lower temperature than normal, raised or lowered blood pressure or an abnormality showin ...

HELLP syndrome HELLP syndrome is a complication of pregnancy; the acronym stands for hemolysis, elevated liver enzymes, and low platelet count. It usually begins during the last three months of pregnancy or shortly after childbirth. Symptoms may include feelin ...

is a type of pre-eclampsia. It is a combination of three medical conditions:

hemolytic anemia Hemolytic anemia or haemolytic anaemia is a form of anemia due to hemolysis, the abnormal breakdown of red blood cells (RBCs), either in the blood vessels (intravascular hemolysis) or elsewhere in the human body (extravascular). This most commonly ...

, elevated

liver enzymes Liver function tests (LFTs or LFs), also referred to as a hepatic panel, are groups of blood tests that provide information about the state of a patient's liver. These tests include prothrombin time (PT/INR), activated partial thromboplastin ti ...

and

low platelet count Thrombocytopenia is a condition characterized by abnormally low levels of platelets, also known as thrombocytes, in the blood. It is the most common coagulation disorder among intensive care patients and is seen in a fifth of medical patients and ...

. ;

Eclampsia Eclampsia is the onset of seizures (convulsions) in a woman with pre-eclampsia. Pre-eclampsia is one of the hypertensive disorders of pregnancy that presents with three main features: new onset of high blood pressure, large amounts of protein in ...

:This is when tonic-clonic seizures appear in a pregnant woman with high blood pressure and proteinuria. Pre-eclampsia and eclampsia are sometimes treated as components of a common syndrome.

Treatment

There is no specific treatment, but is monitored closely to rapidly identify pre-eclampsia and its life-threatening complications (

and eclampsia). Drug treatment options are limited, as many

antihypertensives Antihypertensives are a class of drugs that are used to treat hypertension (high blood pressure). Antihypertensive therapy seeks to prevent the complications of high blood pressure, such as stroke and myocardial infarction. Evidence suggests that r ...

may negatively affect the

fetus A fetus or foetus (; plural fetuses, feti, foetuses, or foeti) is the unborn offspring that develops from an animal embryo. Following embryonic development the fetal stage of development takes place. In human prenatal development, fetal deve ...

Methyldopa Methyldopa, sold under the brand name Aldomet among others, is a medication used for high blood pressure. It is one of the preferred treatments for high blood pressure in pregnancy. For other types of high blood pressure including hypertensive e ...

hydralazine Hydralazine, sold under the brand name Apresoline among others, is a medication used to treat high blood pressure and heart failure. This includes high blood pressure in pregnancy and very high blood pressure resulting in symptoms. It has bee ...

, and

labetalol Labetalol is a medication used to treat high blood pressure and in long term management of angina. This includes essential hypertension, hypertensive emergencies, and hypertension of pregnancy. In essential hypertension it is generally less pr ...

are most commonly used for severe pregnancy hypertension. The fetus is at increased risk for a variety of life-threatening conditions, including

pulmonary hypoplasia Pulmonary hypoplasia is incomplete development of the lungs, resulting in an abnormally low number or size of bronchopulmonary segments or alveoli. A congenital malformation, it most often occurs secondary to other fetal abnormalities that inter ...

(immature lungs). If the dangerous complications appear after the fetus has reached a point of viability, even though still immature, then an early delivery may be warranted to save the lives of both mother and baby. An appropriate plan for labor and delivery includes selection of a hospital with provisions for advanced life support of newborn babies.

Evolutionary considerations

Humans

Gestational hypertension is one of the most common disorders seen in human pregnancies. Though relatively benign on its own, in roughly half of the cases of gestational hypertension the disorder progresses into pre-eclampsia, a dangerous condition that can prove fatal to expectant mothers. However, gestational hypertension is a condition that is fairly rare to see in other animals. For years, it has been the belief of the scientific community that gestational hypertension and pre-eclampsia were relatively unique to humans, although there has been some recent evidence that other primates can also develop similar conditions, albeit due to different underlying mechanisms. The underlying cause of gestational hypertension in humans is commonly believed to be an improperly implanted placenta. Humans have evolved to have a very invasive placenta to facilitate better oxygen transfer from the mother to the fetus, to support the growth of its large brain.

Origins of the placenta

The origins of gestational hypertension may lie with the development of humans' hemochorial placenta. A hemochorial placenta optimizes the amount of oxygen and nutrients that can be absorbed into the fetal blood supply, while at the same time ensuring rapid diffusion of wastes away from the fetus. This hemochorial placenta differs from lower primates' epitheliochorial placentae in the way that it allows the fetal tissues to interact directly with the mother's blood. The hemochorial placenta thereby promotes more rapid diffusion to and from the fetal blood supply. In animals with epitheliochorial placentae such as horses and pigs, the greatest resistance to maternal blood flow in the vascular system was found within the placenta. However, in animals with hemochorial placental structures such as rodents and primates, the vascular resistance in the placenta was low, leading scientists to the conclusion that the greatest resistance to maternal blood flow is found elsewhere in the maternal vascular system. The high vascular resistance outside of the placenta leads to higher maternal blood pressure throughout the body. The fetal cells that implant into the uterine wall are known as the trophoblast. The hemochorial placenta bathes the fetal trophoblast in maternal blood by forming lacunae, or lakes, of the mother's blood that surround fetal tissue. The lacunae are filled by the spiral arteries, which means that the mother's blood pressure is the driving force behind the introduction of new blood, which contains both oxygen and food for the fetus, to the system. It is thought that humans need the increased diffusion provided by the hemochorial placenta in order to grow the large brains compared to their body size that distinguish them from other primates.

Incorrect placental implantation

It is thought that "failings" in normal hemochorial placental structure lead to pre-eclampsia and gestational hypertension. The human placenta implants "earlier, deeper, and more extensively" into the uterine wall, which can potentially lead to many problems that are found in human pregnancies, but not as much in other animals. Miscarriage and pre-eclampsia are both very rare in other species, but are two of the most common pregnancy-related diseases in humans. The genetic roots of gestational hypertension and pre-eclampsia are certain, as women with a family history of the condition are three times more likely to develop it when they are pregnant. One of the potential causes of gestational hypertension and pre-eclampsia is when the trophoblast does not invade far enough into the uterine lining. When the fetus's trophoblast does not fully extend into the uterine wall, the spiral arteries do not become fully converted into low-resistance channels. It has been found that this incomplete conversion of spiral arteries increases the resistance to uterine blood flow during pregnancy, and that this occurrence was associated with gestational hypertension. One potential cause of this incomplete breach of the spiral arteries that leads to gestational hypertension is a mistaken immune response by the maternal tissue, reaction to the alien fetal tissue. Therefore, it is clear that the complication of gestational hypertension has roots in the early implantation of the fetus in the uterine wall, an implantation technique that is unique to humans. The highly invasive placenta that is found in humans is thought to be linked to humans' high circulating levels of the hormones CG and hCG. It has been shown that the higher the levels of these hormones, the deeper the trophoblast's invasion into the uterine wall. Instances of gestational hypertension and pre-eclampsia have been shown to occur when the invasion of the uterine wall is not deep enough, because of lower CG and hCG levels in the mother.

Evolutionary tradeoff

Despite these risks for gestational hypertension, the hemochorial placenta has been favored because of its advantages in the way that it aids in diffusion from mother to fetus later in pregnancy. The bipedal posture that has allowed humans to walk upright has also led to a reduced cardiac output, and it has been suggested that this is what necessitated humans' aggressive early placental structures. Increased maternal blood pressure can attempt to make up for lower cardiac output, ensuring that the fetus's growing brain receives enough oxygen and nutrients. The benefits of being able to walk upright and run on land have outweighed the disadvantages that come from bipedalism, including the placental diseases of pregnancy, such as gestational hypertension. Similarly, the advantages of having a large brain size have outweighed the deleterious effects of having a placenta that does not always convert the spiral arteries effectively, leaving humans vulnerable to contracting gestational hypertension. It is speculated that this was not the case with Neanderthals, and that they died out because their cranial capacity increased too much, and their placentae were not equipped to handle the fetal brain development, leading to widespread pre-eclampsia and maternal and fetal death. Gestational hypertension in the early stages of pregnancy (trimester 1) has been shown to improve the health of the child both in its first year of life, and its later life. However, when the disease develops later in the pregnancy (subsequent trimesters), or turns into pre-eclampsia, there begin to be detrimental health effects for the fetus, including low birth-weight. It has been proposed that fetal genes designed to increase the mother's blood pressure are so beneficial that they outweigh the potential negative effects that can come from pre-eclampsia. It has also been suggested that gestational hypertension and pre-eclampsia have remained active traits due to the cultural capacity of humans, and the tendency for midwives or helpers to aid in delivering babies.

Relevance of evolutionary history

It is the goal of

evolutionary medicine Evolutionary medicine or Darwinian medicine is the application of modern evolutionary theory to understanding health and disease. Modern biomedical research and practice have focused on the molecular and physiological mechanisms underlying heal ...

to find treatments for diseases that are informed by the evolutionary history of a disease. It has been suggested that gestational hypertension is linked to insulin resistance during pregnancy. Both the increase in blood sugar that can lead to gestational diabetes and the increase in blood pressure that can lead to gestational hypertension are mechanisms that mean to optimize the amount of nutrients that can be passed from maternal tissue to fetal tissue. It has been suggested that techniques used to combat insulin insensitivity might also prove beneficial to those with gestational hypertension. Measures to avoid insulin resistance include avoiding obesity before pregnancy, minimizing weight gain during pregnancy, eating foods with low glycemic indices, and exercising.

References

External links

{{DEFAULTSORT:Gestational hypertension Hypertension Health issues in pregnancy Human pregnancy