Pregnancy
Pregnancy (or gestation) is the physiological process in which the living offspring of a woman grows in her body from conception until it can survive outside the body of the mother. A woman's pregnancy is known as pregnant or gravid.
Pregnancy begins with fertilization of the ovum by the sperm, which results in the creation of an egg cell which will divide to become an embryo, then a fetus. It continues until the birth, or its interruption by a natural or artificial abortion (miscarriage).
In humans, pregnancy lasts about 39 weeks, between fertilization and birth. It is divided into three periods of three months each, known as quarters.
But for reasons of convention we are talking weeks of gestation or 41 weeks (corresponding to 39 weeks of gestation and 2 weeks between the first day of last menstruation and fertilization), or even months of pregnancy.
Fertilization
The first stage of pregnancy starts with sex (or intercourse) in which the male gametes (sperm) are issued (for ejaculation) in the vagina. Semen is composed not only sperm but also sugars (mainly fructose), proteins and other substances used to maintain the cellular alive. The human sperm survives about 48 hours in a woman's body (sometimes more). Sperm have a long flagellum (a sort of "tail") they use to move, thus the only human cells provided an organelle of movement. These cells are haploid, having divided during meiosis of germ cells in the testes of the male, and thus only half the chromosomes of cells in the body. The human ejaculate contains between 100 and 300 million sperm (see semen).
The oocyte is the haploid egg cell (ie it contains only half the genetic material) female. Its role is to merge with a sperm and become fertilized zygote which then grow in the uterus and embryo and fetus will become. The egg is created by meiosis in the ovary of the female and remains in a state of suspension until the hormonal fluctuations of the menstrual cycle (peak day 14 hormonal cycle in women, more commonly known as ovulation) cause its release and its release into the fallopian tube. Usually only one egg is released by the menstrual cycle (release of two ova fertilization and later gives birth to "fraternal twins, ie twins from two different eggs fertilized by two different sperm).
During ovulation, the fringe (fimbriae) of the fallopian tubes covers the ovary to receive the egg released. In the event of fertilization, the sperm meets egg usually in the fallopian tube at its outer third (in the bulb), the sperm must pass through the upper vagina, cervix, uterus and the fallopian tube before reaching the egg, which is a considerable distance compared with the size of the sperm.
Sperm that do try to fertilize the egg. Each sperm cell door at the end head, contained in a vacuole, lytic enzymes used to dissolve a portion of the outer layer of the egg. This step, when it reaches its end, can take about 20 minutes. Once merged the egg with a sperm cell, its cell wall composition changes, thus inhibit the penetration of a spermatozoon. The fusion of nuclei of egg and sperm creates a diploid cell (ie including all the genetic material necessary for its growth, half of maternal origin and a paternal half), supplementing the first stage of pregnancy.
Alternative means of fertilization, including artificial insemination and in vitro fertilization, are sometimes used in cases of infertility. In France, access to medically assisted procreation impose the need of a couple living in age, sex, may have at least two years of cohabitation.
The outsourcing is ectogenese as oviparous. It is not (yet) to the point technically.
Preimplantation period
At this moment the zygote is a single totipotent stem cell (called cell-egg) with the ability to create a whole organism. Cell division by mitosis is the next process: each cell splits to produce another diploid cell. The zygote divides to produce two smaller cells, called blastomeres, roughly every 20 hours. These cells redivisent about 3 times (16 cells). This cluster of cells, said the morula (because of its appearance, which can be closer to a blackberry) leaves the fallopian tube and enters the uterus.
Postimplantation
The cells developed around the blastocèle distribute a fluid cavity in the middle of the cells. The cells become, as their division by mitosis, becoming smaller. This structure includes cells and zygotic blastocèle called the blastocyst. The cells start to differentiate between cells inside and outside the blastocyst. In 24 to 48 hours, the wall of the blastocyst, the zona pellucida, is broken. The exterior of the blastocyst cells begin to secrete an enzyme which erodes the epithelium of the uterus and creates a site for implantation. The blastocyst also secretes chorionic gonadotropin (HCG), a hormone that stimulates the corpus luteum of the ovary of the mother to produce progesterone, which maintains the lining of the uterus to nourish the embryo. The glands in the uterine lining grows in response to blastocyst, and the hair growth is stimulated in the region, ensuring the provision of vital nutrients and oxygen to the blastocyst.
The diagnosis of pregnancy is by research blood or urine fraction beta of the chorionic gonadotropin, known as beta-HCG. The urine pregnancy tests available in pharmacies offer a qualitative assay of the hormone, their reliability is 90 to 99%. The determination of blood, quantitative beta-HCG allows a diagnosis of certainty and timing of early pregnancy (the rate of this hormone double every 48 hours in early pregnancy).
Circulatory system of the placenta
The cells around the blastocyst begins to destroy cells of the uterine lining, producing small puddles of blood and stimulating the production of new capillaries. This is the first step in the development of the placenta. The interior of the blastocyst cells grow rapidly and form two layers. The top layer will become the embryo and amniotic cavity and the bottom layer will create a small "bag", the vitelline vesicle. A few days later, chorionic villi of placenta anchor the blastocyst in the uterus. A blood system develops in relation to the placenta, near the site of implantation: the future area of exchange between the maternal circulation and fetal circulation is being established. Vitelline vesicle in the blastocyst begins to produce the first cell (or "red"). During the next 24 hours, connective tissue develops between the placenta and fetus, which later becomes the umbilical cord, connecting the ventral side of the embryo to the placenta (it contains a vein and two arteries).
Cellular differentiation
Then, a thin layer of cells develops at the surface of the embryo, indicating the beginning of gastrulation. It is a process in which the three leaflets of the fetus, the ectoderm, the mesoderm (or mesoderm) and endoblaste, are developing. The layer of cells begins by stimulating the growth of the endoblaste and mesoderm, and ectoderm begins to grow rapidly due to chemicals produced by stimulating the mesoderm above it.
These three layers will develop to form all structures of the body of the embryo. The endoblaste give the mouth, tongue, digestive tract, lungs, bladder and several glands. The mesoderm gives the lungs, heart, spleen, and the system of reproduction and excretion. It will also assist in the production of blood lines. The ectoderm (now neurectoblaste at the 4th week) will become the skin, nails, hair and hair, eyes, internal and external surface of the ears, nose, sinuses, mouth, anus, teeth, mammary glands, and all parts of the nervous system (brain, spinal cord, nerves).
About 18 days after fertilization, the embryo produced most forms of tissue he needs. It is shaped like a pear, with the head (the cluster head) larger than the tail (the caudal pole). The nervous system is one of the first structures to develop. Within the neurectoblaste, a vacuum is created which then merged banks amounted to a tube at the origin of the neural groove, extended cephalad pole of the caudal pole of the embryo, the first axis of the Organization of the Future nervous system. The blood takes place from the mesoderm produces networks allow the distribution of blood in the embryo, blood cells are in production and in circulation in the embryo. Secondary vessels grow in and around the placenta to fill the growing needs of the embryo in nutrients. The blastocèle produces blood cells and cells that become blood vessels. Endocardial cells develop in the mesoderm, they are intended to form the inner layers of the heart.
Approximately 24 days after fertilization goes into a primitive heart (currently a simple tube-shaped S), which begins to beat and circulate blood vessels in infancy.
The diagnosis of pregnancy
The diagnosis of pregnancy in the laboratory or at home:
* Principle: Based on the detection in urine or plasma of pregnant women of a specific hormone produced by the placental tissue: the hormone chorionic gonadotropin (HCG) glycoprotein composed of two subunits alpha and beta.
It appears very rapidly in the blood and urine after fertilization, the concentration increases the first three months of pregnancy, then decreases and disappears after childbirth. The radio-immunological determination of the fraction of beta HCG practiced in laboratory can be positive from the 6th day of fertilization.
* Biological Tests: The first tests carried out on the hormone HCG using an animal to which the urine of pregnant women presumed was injected.
The presence of HCG causing biological changes, would conclude that the existence of pregnancy (test-Mainini Galli on the toad to Ascheimzondeck on mice, rabbits Friedman on, etc..) Abandoned.
* Immunologic tests: More early more precise and less expensive.
Based on the visualization of the reaction occurring between a monoclonal antibody (anti-HCG antibodies obtained by immunization in animals) and an antigen. In the presence of HCG from the urine of pregnant women, the anti-HCG antibody reacts with the antigen. Several methods: agglutination test, test of inhibition of hemaglutination, colorimetric immunoenzymatic test, test immunoconcentration, test immunoconcentration climb.
* Personal Tests: (sold in pharmacies since 1973, not sold in supermarkets
Not reimbursed by Social Security MARKS: G.test (Map or "Sceen"): the first were made available to women in 1973. They are available from the day of the alleged rules. The result is 2 to 5 minutes by the appearance of a pink line (negative) or 2 pink lines (positive result).
General
The principles set out below relate only to the monitoring of pregnancy in France. This monitoring is marked by a strong intervention of the State, manifested by decrees and regulations.
Two examples are particularly striking: France is the only country in the world where screening for toxoplasmosis during pregnancy is mandatory. Many countries do not or only testing among populations at risk.
The same goes for the risk assessment of trisomy 21 (Down syndrome) during pregnancy by the determination of HCG and alpha-fetoprotein although other methods are more efficient. This screening is the subject of regulations published in the Official Journal.
The number of ultrasound during pregnancy is 3 in France but only one ultrasound, Norway, is used systematically to 18 weeks (the legal limit of the medical in this country is 22 weeks), others being present only on signs of Appeal.
The purpose of regular monitoring is the early detection of obstetric pathologies (stunted intrauterine, arterial hypertension of pregnancy, for example). Of serology were made on a regular basis to track certain infectious diseases that can cause embryopathy or fœtopathie, particularly among women not immunized. Search for irregular agglutinins every month in women rhesus negative.
Screening for trisomy 21 by the determination of HCG and alpha-fetoprotein should be offered routinely to all pregnant women (but not mandatory).
Of biological or bacteriological examinations are recommended at specific moments of pregnancy.
An examination of the cervix through the vaginal is usually performed during normal pregnancies to detect theoretically the risk of premature birth. But the vaginal is not part of the monitoring of normal pregnancies in many countries in Europe (England, Spain, Netherlands, Finland, Sweden, Denmark) with rates of premature identical or lower than the France. Finally, some countries consider this review as hazardous (Norway) and as such as medical malpractice.
The existence of a consultation for couples before the start of a pregnancy would be highly desirable: the large number of couples in which one element is a carrier of a genetic disease requires to inform them of the possibilities of prenatal diagnosis . Prenatal diagnosis often requires effective to know the exact mutation involved. The prevention of certain anomalies of the central nervous system involves taking vitamins several weeks before fertilization.
First consultation
Once a woman knows her pregnancy, it is desirable that it enjoys a consultation within two months. During this first consultation will be carried out:
* An interview:
1. Searching for family history of genetic diseases or abnormalities may be eligible for prenatal diagnosis and genetic counseling. The search for antecedent familial thrombo-embolism is also important for the detection of thrombophilia as pregnancy is a high thrombogenic risk;
2. The recurrence of certain malformations family is known. Some defects can be avoided by a preventive treatment such as prescription of folic acid for prevention of spina bifida;
3. The number and the normal pregnancy or not, their term and the weight of children at birth will be noted. Finally, the mode of delivery and the existence of complications complete the examination to distinguish pregnancies at risk;
4. The existence of maternal disease or taking medicines (regular or occasional) before and in early pregnancy should be taken into account because of possible side effects on the unborn child. It is important to decide on treatment course, the opportunity to continue to interrupt or modify them. The impact of pathology on pregnancy and pregnancy on the disease should also be mentioned;
* A clinical examination:
1. A review of cardiovascular disease with cardiac auscultation is made;
2. Weight and blood pressure will be increased;
* The smear screening:
1. The smear screening for cancer of the cervix will be performed in all women do not receive regular gynecologic follow-up;
* The dating of pregnancy:
It has a double interest, medical and legal, in effect:
*
o Medically, it can detect abnormalities of fetal development, abnormal amniotic fluid (hydramnios, oligamnios), to know the expected date of completion of pregnancy (41 weeks of gestation or 39 weeks of pregnancy) and ask the diagnosis exceeded term or prematurity,
o Legally, it influences a potential application of abortions (legal maximum term of 14 SA in France), the declaration of pregnancy (SA 16 at the latest), the viability of the fetus (spontaneous interruption of pregnancy beyond the 22nd SA allows to declare a stillborn child at the civil status)
o methods of dating of pregnancy:
1. In the interview, from the first day of the last menstrual period (which determines the number of weeks of amenorrhea). The conception occurs 14 days later, at the time of ovulation,
2. Through ultrasound, measuring the cranio-caudal length of the embryo. This method can be the 7th to the 12th SA, and is accurate to about 3 days. It rests on a basic concept: in the first quarter, growth is the same for all embryos (it is dependent than uterine factors, not genetic or hormonal)
* Systematic examinations: toxoplasmosis and rubella serology (in the absence of proof of immunization prior), serology for syphilis, blood group, rhesus group, search for irregular agglutinins, Kell phenotype, urinary strip (glucose search , nitrites, leukocytes and ketones in the urine);
* Other tests are sometimes prescribed blood (early detection of anemia), search for hepatitis B and C and AIDS;
* Advice for healthy living are:
1. Have a balanced diet rich in calcium and vegetables, avoid milk and cheese from raw milk (prevention of listeriosis), avoid eating raw meat.
2. In case of no immunization against toxoplasmosis, it is advisable to avoid contact with cats and their feces, wash fruits and vegetables, well cooked meat,
3. Smoking cessation and abstinence complete vis-a-vis alcohol (see fetal alcohol syndrome). If necessary, refer the patient to consult anti-tobacco
4. Maintaining an appropriate sporting activity at the end of pregnancy. Weight gain is twelve kilograms on average in pregnancy.
5. In France: declaration of pregnancy before the 16th week of gestation to social security and the family allowance fund.
Read also Embryo
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