September 19, 2019
Gestational hypertension

Gestational hypertension

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. References

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