डबल मार्कर टेस्ट की बात करें, तो यह गर्भधारण की पहली तिमाही पर किया जाने वाला रक्त परीक्षण है। आमतौर पर इसे गर्भधारण के 10वें और 14वें सप्ताह के बीच किया जाता है। इसमें एनोप्लॉयडी (गुणसूत्र की असामान्य मात्रा) गर्भावस्था का पता लगाया जाता है। खास यह है कि डबल मार्कर टेस्ट नॉन-इनवेसिव स्क्रीनिंग (बिना किसी कट मार्क के किया जाने वाला परीक्षण) है। इस टेस्ट के जरिए डाउनग्रेड सिंड्रोम (ट्राइसोमी 21), एडवर्ड सिंड्रोम (ट्राइसोमी 18) और पटाउ सिंड्रोम (ट्राइसोमी 13) जैसे क्रोमोसोम (गुणसूत्र) का पता लगाया जाता है । क्रोमोसोम में किसी प्रकार की कमी होने पर भ्रूण के विकास में बाधा आ सकती है या फिर जन्म के बाद भविष्य में शिशु को किसी प्रकार की स्वास्थ्य समस्या का सामना करना पड़ सकता है। कई जीन के समावेश को क्रोमोसोम यानी गुणसूत्र बोला जाता है।
आगे लेख में हम यह जानेंगे कि किन स्थितियों में डबल मार्कर टेस्ट की आवश्यकता पड़ती है और इसे क्यों किया जाता है।
डबल मार्कर टेस्ट क्यों किया जाता है?
जिन गर्भवती महिलाओं को विशेष प्रकार के गंभीर जोखिम की श्रेणी में शामिल किया जाता है, उन्हें डबल मार्कर टेस्ट कराने की आवश्यकता होती है। उनके इन गंभीर जोखिमों को देखते हुए ही चिकित्सक उन्हें डबल मार्कर टेस्ट कराने की सलाह देते हैं। आइए, एक नजर डालते हैं उन जोखिमों पर जिनके कारण गर्भवती महिला को डबल मार्कर टेस्ट कराना जरूरी हो जाता है ।
The placenta begins to develop upon implantation of the blastocyst into the maternal endometrium. The outer layer of the blastocyst becomes the trophoblast, which forms the outer layer of the placenta. This outer layer is divided into two further layers: the underlying cytotrophoblast layer and the overlying syncytiotrophoblast layer. The syncytiotrophoblast is a multinucleated continuous cell layer that covers the surface of the placenta. It forms as a result of differentiation and fusion of the underlying cytotrophoblast cells, a process that continues throughout placental development. The syncytiotrophoblast (otherwise known as syncytium), thereby contributes to the barrier function of the placenta.
The placenta grows throughout pregnancy. Development of the maternal blood supply to the placenta is complete by the end of the first trimester of pregnancy week 14 (DM).
Placental circulation
Maternal blood fills the intervillous space, nutrients, water, and gases are actively and passively exchanged, then deoxygenated blood is displaced by the next maternal pulse.
Maternal placental circulation
In preparation for implantation of the blastocyst, the endometrium undergoes decidualization. Spiral arteries in the decidua are remodeled so that they become less convoluted and their diameter is increased. The increased diameter and straighter flow path both act to increase maternal blood flow to the placenta. There is relatively high pressure as the maternal blood fills intervillous space through these spiral arteries which bathe the fetal villi in blood, allowing an exchange of gases to take place. In humans and other hemochorial placentals, the maternal blood comes into direct contact with the fetal chorion, though no fluid is exchanged. As the pressure decreases between pulses, the deoxygenated blood flows back through the endometrial veins.
Maternal blood flow is approximately 600–700 ml/min at term.
This begins at day 5 - day 12
Fetoplacental circulation
Deoxygenated fetal blood passes through umbilical arteries to the placenta. At the junction of umbilical cord and placenta, the umbilical arteries branch radially to form chorionic arteries. Chorionic arteries, in turn, branch into cotyledon arteries. In the villi, these vessels eventually branch to form an extensive arterio-capillary-venous system, bringing the fetal blood extremely close to the maternal blood; but no intermingling of fetal and maternal blood occurs ("placental barrier"
The fetoplacental circulation is vulnerable to persistent hypoxia or intermittent hypoxia and reoxygenation, which can lead to generation of excessive free radicals. This may contribute to pre-eclampsia and other pregnancy complications. It is proposed that melatonin plays a role as an antioxidant in the placenta.
This begins at day 17 - day 22
Microbiome
The placenta is traditionally thought to be sterile, but recent research suggests that a resident, non-pathogenic, and diverse population of microorganisms may be present in healthy tissue. However, whether these microbes exist or are clinically important is highly controversial and is the subject of active research.
Functions
Nutrition and gas exchange
The placenta intermediates the transfer of nutrients between mother and fetus. The perfusion of the intervillous spaces of the placenta with maternal blood allows the transfer of nutrients and oxygen from the mother to the fetus and the transfer of waste products and carbon dioxide back from the fetus to the maternal blood. Nutrient transfer to the fetus can occur via both active and passive transport. Placental nutrient metabolism was found to play a key role in limiting the transfer of some nutrients. Adverse pregnancy situations, such as those involving maternal diabetes or obesity, can increase or decrease levels of nutrient transporters in the placenta potentially resulting in overgrowth or restricted growth of the fetus.
Excretion
Waste products excreted from the fetus such as urea, uric acid, and creatinine are transferred to the maternal blood by diffusion across the placenta.
Immunity
IgG antibodies can pass through the human placenta, thereby providing protection to the fetus in utero. This transfer of antibodies begins as early as the 20th week of gestational age, and certainly by the 24th week.[27] This passive immunity lingers for several months after birth, thus providing the newborn with a carbon copy of the mother's long-term humoral immunity to see the infant through the crucial first months of extrauterine life. IgM, however, cannot cross the placenta, which is why some infections acquired during pregnancy can be hazardous for the fetus.
Furthermore, the placenta functions as a selective maternal-fetal barrier against transmission of microbes. However, insufficiency in this function may still cause mother-to-child transmission of infectious diseases.
Endocrine function
·The first hormone released by the placenta is called the human chorionic gonadotropin hormone. This is responsible for stopping the process at the end of menses when the Corpus luteum ceases activity and atrophies. If hCG did not interrupt this process, it would lead to spontaneous abortion of the fetus. The corpus luteum also produces and releases progesterone and estrogen, and hCG stimulates it to increase the amount that it releases. hCG is the indicator of pregnancy that pregnancy tests look for. These tests will work when menses has not occurred or after implantation has happened on days seven to ten. hCG may also have an anti-antibody effect, protecting it from being rejected by the mother’s body. hCG also assists the male fetus by stimulating the testes to produce testosterone, which is the hormone needed to allow the sex organs of the male to grow.
·Progesterone helps the embryo implant by assisting passage through the fallopian tubes. It also affects the fallopian tubes and the uterus by stimulating an increase in secretions necessary for fetal nutrition. Progesterone, like hCG, is necessary to prevent spontaneous abortion because it prevents contractions of the uterus and is necessary for implantation.
·Estrogen is a crucial hormone in the process of proliferation. This involves the enlargement of the breasts and uterus, allowing for growth of the fetus and production of milk. Estrogen is also responsible for increased blood supply towards the end of pregnancy through vasodilation. The levels of estrogen during pregnancy can increase so that they are thirty times what a non-pregnant woman mid-cycles estrogen level would be.
The placenta and fetus may be regarded as a foreign body inside the mother, and needs to be protected from the normal immune response of the mother that would cause it to be rejected. The placenta and fetus are thus treated as sites of immune privilege, with immune tolerance.
For this purpose, the placenta uses several mechanisms:
·There is presence of small lymphocytic suppressor cells in the fetus that inhibit maternal cytotoxic T cells by inhibiting the response to interleukin 2.
However, the Placental barrier is not the sole means to evade the immune system, as foreign fetal cells also persist in the maternal circulation, on the other side of the placental barrier.
Other
The placenta also provides a reservoir of blood for the fetus, delivering blood to it in case of hypotension and vice versa, comparable to a capacitor.
Ultrasound image of human placenta and umbilical cord (color Doppler rendering) with central cord insertion and three umbilical vessels, at 20 weeks of pregnancy
Retinitis pigmentosa
(RP) is a term for a group of eye diseases that can lead to loss of sight.
What they have in common is a coloring your doctor sees when he looks at your
retina -- a bundle of tissue at the back of your eye. When you have RP, cells
in the retina called photoreceptors don’t work the way they're supposed to, and
over time, you lose your sight.
It’s a rare disorder that’s passed from parent to child.
Only 1 out of every 4,000 people get it. About half of all people with RP have
a family member who also has it.
The retina has two types of cells that gather light: rods
and cones. The rods are around the outer ring of the retina and are active in
dim light. Most forms of retinitis pigmentosa affect the rods first. Your night vision and your ability to see to the side
-- peripheral vision -- go away.
Cones are mostly in the center of your retina. They help
you see color and fine detail. When RP affects them, you slowly lose your
central vision and your ability to see color.
Symptoms
Retinitis
pigmentosa usually starts in childhood. But exactly when it starts and how
quickly it gets worse varies from person to person. Most people with RP lose
much of their sight by early adulthood. Then by age 40, they are often legally blind.
Because rods are usually affected first, the first symptom
you may notice is that it takes longer to adjust to darkness (called “night blindness). For example, you may notice it when
you walk from bright sunshine into a dimly lit theater. You may trip over
objects in the dark or not be able to drive at night.
You may lose your peripheral vision at the same time or
soon after your night vision declines. You may get "tunnel vision,"
which means you can’t see things to the side without turning your head.
In later stages, your cones may be affected. That will make
it harder for you to do detail work, and you may have trouble seeing colors. It’s rare, but sometimes
the cones die first.
You might find bright lights uncomfortable -- a symptom
your doctor may call photophobia. You also may start to see flashes of
light that shimmer or blink. This is called photopsia.
ØHuman chorionic gonadotropin (hCG) hCG is an important hormone in early pregnancy. It’s produced by the placenta
after implantation, and
supports the function of the corpus luteum. During the early weeks of pregnancy, the corpus luteum produces progesterone.
After 8-12 weeks, the placenta takes over. Progesterone stimulates growth of
the blood vessels that supply the womb lining. As with progesterone, the corpus luteum produces oestrogen in the early stages
of pregnancy before the placenta takes over. Oestrogen is actually a collective
group of similar compounds: oestrone, oestradiol, and oestriol. Prolactin is the main hormone needed to trigger the production of breast milk.
It enlarges the mammary glands to prepare for this (though as previously noted
progesterone levels prevent lactation until the baby is born). Relaxin levels are highest during the first trimester of pregnancy, but it is
present throughout. It has several roles, including prohibiting contraction of
the uterine muscles to prevent premature birth. Oxytocin only appears in significant amounts towards the end of pregnancy,
though it is present in lower amounts before this. Its levels rise when labour
starts, triggering contractions. ØThe corpus luteum is a temporary structure
in the ovaries which produces other key hormones during early pregnancy. ØhCG is also the hormone detected by
pregnancy tests. Its concentration increases from conception and peaks 8–11
weeks after. For the first few days after conception its levels are too low to
detect with pregnancy tests, but after implantation its
levels double
every 48 hours. ØProgesterone ØIt also stimulates the lining to release
nutrients, providing nourishment for the early embryo. Additionally,
progesterone inhibits contraction of the smooth muscle of the uterus so that it
grows as the baby does. ØProgesterone levels continue to rise as
the pregnancy progresses. Along with oestrogen, it promotes the growth of
breast tissue and milk duct development. Progesterone prevents lactations
during pregnancy, which only starts when levels drop after birth. This hormone
also plays an important role in preparation for birth: it strengthens the
pelvic wall muscles required for labour. ØNoticing increased hair growth during
pregnancy? That’s also due to progesterone! ØOestrogen ØOestrogen helps the uterus grow and
maintains its lining. It supports foetal development, including the development
of organs and bodily systems. It also activates and regulates the production of
other important pregnancy hormones. ØProlactin ØProlactin has other roles unrelated to milk
production. It contributes to the development of the foetal lungs and brain,
and also to the mother’s immune system tolerating the foetus. ØRelaxin ØRelaxin’s name gives a clue to its more
important roles. It relaxes blood vessels, increasing blood flow to the
placenta and kidneys. This helps the mother’s body cope with the increased
demand for oxygen and nutrients from the developing baby. ØRelaxin also helps the mother’s body
prepare for birth. It relaxes joints in the pelvis and softens and widens the
cervix to make delivery of the baby easier. ØOxytocin ØIf labour doesn’t start naturally,
oxytocin (or synthetic equivalents) can be used to induce it.
ØHuman chorionic gonadotropin (hCG)
hCG is an important hormone in early pregnancy. It’s produced by the placenta
after implantation, and
supports the function of the corpus luteum.
ØThe corpus luteum is a temporary structure
in the ovaries which produces other key hormones during early pregnancy.
ØhCG is also the hormone detected by
pregnancy tests. Its concentration increases from conception and peaks 8–11
weeks after. For the first few days after conception its levels are too low to
detect with pregnancy tests, but after implantation its
levels double
every 48 hours.
ØProgesterone
During the early weeks of pregnancy, the corpus luteum produces progesterone.
After 8-12 weeks, the placenta takes over.
Progesterone stimulates growth of
the blood vessels that supply the womb lining.
ØIt also stimulates the lining to release
nutrients, providing nourishment for the early embryo. Additionally,
progesterone inhibits contraction of the smooth muscle of the uterus so that it
grows as the baby does.
ØProgesterone levels continue to rise as
the pregnancy progresses. Along with oestrogen, it promotes the growth of
breast tissue and milk duct development. Progesterone prevents lactations
during pregnancy, which only starts when levels drop after birth. This hormone
also plays an important role in preparation for birth: it strengthens the
pelvic wall muscles required for labour.
ØNoticing increased hair growth during
pregnancy? That’s also due to progesterone!
ØOestrogen
As with progesterone, the corpus luteum produces oestrogen in the early stages
of pregnancy before the placenta takes over. Oestrogen is actually a collective
group of similar compounds: oestrone, oestradiol, and oestriol.
ØOestrogen helps the uterus grow and
maintains its lining. It supports foetal development, including the development
of organs and bodily systems. It also activates and regulates the production of
other important pregnancy hormones.
ØProlactin
Prolactin is the main hormone needed to trigger the production of breast milk.
It enlarges the mammary glands to prepare for this (though as previously noted
progesterone levels prevent lactation until the baby is born).
ØProlactin has other roles unrelated to milk
production. It contributes to the development of the foetal lungs and brain,
and also to the mother’s immune system tolerating the foetus.
ØRelaxin
Relaxin levels are highest during the first trimester of pregnancy, but it is
present throughout. It has several roles, including prohibiting contraction of
the uterine muscles to prevent premature birth.
ØRelaxin’s name gives a clue to its more
important roles. It relaxes blood vessels, increasing blood flow to the
placenta and kidneys. This helps the mother’s body cope with the increased
demand for oxygen and nutrients from the developing baby.
ØRelaxin also helps the mother’s body
prepare for birth. It relaxes joints in the pelvis and softens and widens the
cervix to make delivery of the baby easier.
ØOxytocin
Oxytocin only appears in significant amounts towards the end of pregnancy,
though it is present in lower amounts before this. Its levels rise when labour
starts, triggering contractions.
ØIf labour doesn’t start naturally,
oxytocin (or synthetic equivalents) can be used to induce it.
hCG is an important hormone in early pregnancy. It’s produced by the placenta
after implantation, and
supports the function of the corpus luteum.
During the early weeks of pregnancy, the corpus luteum produces progesterone.
After 8-12 weeks, the placenta takes over.
Progesterone stimulates growth of
the blood vessels that supply the womb lining.
As with progesterone, the corpus luteum produces oestrogen in the early stages
of pregnancy before the placenta takes over. Oestrogen is actually a collective
group of similar compounds: oestrone, oestradiol, and oestriol.
Prolactin is the main hormone needed to trigger the production of breast milk.
It enlarges the mammary glands to prepare for this (though as previously noted
progesterone levels prevent lactation until the baby is born).
Relaxin levels are highest during the first trimester of pregnancy, but it is
present throughout. It has several roles, including prohibiting contraction of
the uterine muscles to prevent premature birth.
Oxytocin only appears in significant amounts towards the end of pregnancy,
though it is present in lower amounts before this. Its levels rise when labour
starts, triggering contractions.
ØThe corpus luteum is a temporary structure
in the ovaries which produces other key hormones during early pregnancy.
ØhCG is also the hormone detected by
pregnancy tests. Its concentration increases from conception and peaks 8–11
weeks after. For the first few days after conception its levels are too low to
detect with pregnancy tests, but after implantation its
levels double
every 48 hours.
ØProgesterone
ØIt also stimulates the lining to release
nutrients, providing nourishment for the early embryo. Additionally,
progesterone inhibits contraction of the smooth muscle of the uterus so that it
grows as the baby does.
ØProgesterone levels continue to rise as
the pregnancy progresses. Along with oestrogen, it promotes the growth of
breast tissue and milk duct development. Progesterone prevents lactations
during pregnancy, which only starts when levels drop after birth. This hormone
also plays an important role in preparation for birth: it strengthens the
pelvic wall muscles required for labour.
ØNoticing increased hair growth during
pregnancy? That’s also due to progesterone!
ØOestrogen
ØOestrogen helps the uterus grow and
maintains its lining. It supports foetal development, including the development
of organs and bodily systems. It also activates and regulates the production of
other important pregnancy hormones.
ØProlactin
ØProlactin has other roles unrelated to milk
production. It contributes to the development of the foetal lungs and brain,
and also to the mother’s immune system tolerating the foetus.
ØRelaxin
ØRelaxin’s name gives a clue to its more
important roles. It relaxes blood vessels, increasing blood flow to the
placenta and kidneys. This helps the mother’s body cope with the increased
demand for oxygen and nutrients from the developing baby.
ØRelaxin also helps the mother’s body
prepare for birth. It relaxes joints in the pelvis and softens and widens the
cervix to make delivery of the baby easier.
ØOxytocin
ØIf labour doesn’t start naturally,
oxytocin (or synthetic equivalents) can be used to induce it.
