Gestational hypertension or pregnancy-induced hypertension is the
development of new hypertension in a pregnant woman after 20 weeks gestation
without the presence of protein in the urine or other signs of preeclampsia.
Hypertension is defined as greater than 140/90 mm Hg.
Conditions There exist several hypertensive states
of pregnancy: Gestational hypertension
Gestational hypertension is usually defined as having a blood pressure
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. Preeclampsia
Pre-eclampsia is gestational hypertension plus proteinuria. Severe
preeclampsia involves a blood pressure greater than 160/110, with additional
medical signs and symptoms. HELLP syndrome is a type of preeclampsia. It
is a combination of three medical conditions: hemolytic anemia, elevated
liver enzymes and low platelet count. Eclampsia
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.
Risk factors Maternal causes
Obesity Age 35 years or more.
Past history of D.M,Hypertension and Renal diseases.
Adolescent pregnancy. New paternity.
Thrombophilias Having donated a kidney.
Pregnancy Multiple gestation
Placental abnormalities: 1. Hyperplacentosis: Excessive exposure
to chorionic villi. 2. Placental ischemia.
Family history Family history of pre-eclampsia.
African American race Treatment
There is no specific treatment, but is monitored closely to rapidly identify
pre-eclampsia and its life-threatening complications.
Drug treatment options are limited, as many antihypertensives may negatively
affect the fetus. Methyldopa, hydralazine, and labetalol are most
commonly used for severe pregnancy hypertension.
The fetus is at increased risk for a variety of life-threatening conditions,
including pulmonary hypoplasia. 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 preeclampsia, 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 preeclampsia were relatively unique to
humans, although there has been some recent evidence that other primates can
also suffer from 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
preeclampsia 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 preeclampsia
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 preeclampsia are certain, as women with a family history
of the condition are three times more likely to suffer from it when they are
pregnant. One of the potential causes of
gestational hypertension and preeclampsia is when the trophoblast
does not invade far enough into the uterine lining. When the fetus’
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 preeclampsia 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 preeclampsia and maternal and fetal
death. Gestational hypertension in the early
stages of pregnancy 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, or turns into preeclampsia, 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 preeclampsia. It has also been suggested that gestational
hypertension and preeclampsia 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 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 suffering
from gestational hypertension. Measures to avoid insulin resistance include
avoiding obesity before pregnancy, minimizing weight gain during pregnancy,
eating foods with low glycemic indexes, and exercising.
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