You need not be fasting or special care to make this analysis. There are two types of tests you can do to find out if you are pregnant: urine and blood. They are intended to detect the level of the hormone HCG (human chorionic hormone gonatrofina). The difference between them is that the urine test indicates if you are pregnant or not, while the blood test (serum) can indicate what stage of pregnancy you are through the variation of the indicative value between two tests. In the urine the ...
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You need not be fasting or special care to make this analysis. There are two types of tests you can do to find out if you are pregnant: urine and blood. They are intended to detect the level of the hormone HCG (human chorionic hormone gonatrofina). The difference between them is that the urine test indicates if you are pregnant or not, while the blood test (serum) can indicate what stage of pregnancy you are through the variation of the indicative value between two tests. In the urine the qualitative test is intended solely to the diagnosis of pregnancy which is a test whose result is yes or no, as in serum, the test is quantitative. This test is not only done to detect pregnancy, among others it may be used as a tumor marker. However values greater than 5-10 are considered positive for pregnancy (see reference values in analytical bulletin).
Prenatal Screening
Currently a test performed from a mother's blood sample allows us to evaluate the risk of trisomy 21 and other fetal chromosomal abnormalities, and also open neural tube defects (NTD). This test, being simple and noninvasive, must be be offered to all women, regardless of age: it is the prenatal biochemical screening. During pregnancy, it is necessary to monitor the health of the mother and fetus. The biochemical screening tests have to be performed at the right time:
-1st Quarter: between the 11th and 14th weeks of pregnancy
-2nd Quarter: between the 14th and 18th week of pregnancy
In any of the tests carried out in the laboratory the harvest of the maternal blood is made in the arm to ensure accuracy in the result. The sting for harvest in the finger is not rigorous in terms of results, providing a very high number of false positives. Fasting is not necessary.
Explanation of the Prenatal Screening
Risk
After blood collection, the result appears expressed at risk (eg 1 in 500, 1 in 100) and the pregnant that made the screening is classified into groups: high risk positive screening; Low risk negative screening. The risk is a possibility of an abnormality existing. So, if the risk is 1 in 50 (1:50), it means that in 50 women, with their age, the same weeks of pregnancy and the same biochemical and ultrasound profile, one can have a baby with an abnormality. You should discuss with your doctor about what to adopt. If the risk is high, you can choose an amniocentesis. Generally, a high risk is considered exceeding 1/300, which corresponds to the natural risk of a woman of 36 years. The risk that the fetus really has to be born with trisomy 21 is however low, since most of the positives are false positives, hence the importance of having a method that gives us a low number of positive, lest they are effected amniocentesis unnecessarily.
Positive screening
If your exam reveals a positive screening, it means that you were selected to eventually perform an invasive method, by the higher probability of having a fetus with a malformation. Remember however that most babies are healthy, and do not create anxiety. Most of the results with a positive screening do not register any anomaly at birth. Screening serves inside the population of all pregnant women, to show us those that should eventually make amniocentesis, by the risk that this technique has and therefore unjustified to be done in all women. Also remember that amniocentesis does not detect all the problems that the fetus may have only chromosomal abnormalities. So always have a positive thinking and be calm.
Negative screening
If this test has a negative screening, it means that the probability of having a fetus with such defects is low, but does not ensure a normal baby. The screening method is excellent with a detection rate of about 97%.
1st Quarter
The biochemical screening for the 1st quarter is between the 11th and 13th week + 6 days after the last menstrual period, with an ultrasound exam and a blood test. The test calculates the risk in cases of trisomy 21,18 and 13 being able to detect other anomalies in embryos gestation.
Biochemical analysis measures two substances in the mother's blood, the Plasma Protein Associated with Pregnancy (PAPP_A and beta-subunit free of chorionic gonadotropin (beta-HCG free). The ultrasound exam done by a doctor determines the gestational age accurately, measures the thickness of the subcutaneous space between the skin and the soft tissue covering the fetal nape, Nuchal Translucency (NT) and verifies the presence of the nasal bone (NB) .It is a non-invasive test that evaluates the embryonic anatomy and by a specific software is also calculated a risk of trisomy 21 and other malformations.
Early screening avoids additional stress load for parents and decreases the number of late abortions for chromosomal defects, which carries strong emotional costs.
The risk of trisomy 21, very low in young women increases with age, particularly after 35 years. However, most children with trisomy 21 are born to young women, because they are the ones that have more children. The calculation of the increased risk of trisomy takes into account factors such as gestational age and maternal ethnicity and the mother's weight, the presence of diabetes, tobacco use, and cases of chromosomal deficiency before pregnancy.
The chromosomal detection rate using maternal age + TN + ON + free beta-hCG + PAPP-A is about 97% (about 3% false positives).
2nd Quarter
Held between the 14th and the 18th week after the last menstrual period. We can make the 2nd quarter screening until the 22nd week, but the sensitivity of the method is less starting the 18th week. If the risk is high, an amniocentesis is proposed to ensure that the fetus has a normal karyotype (98% of cases). If the fetus has Trisomy 21 an interruption of pregnancy can be carried out if that is the wish of the parents.
Maternal serum markers for the 2nd quarter also allow to calculate the risk of open Neural Tube Defects (NTDs), allowing you to perform an earlier ultrasound than the morphological that would just be made at the 22nd - 24th week, for viewing of any defect of the neural tube most likely seen in the ultrasound starting from the 16th week, so that if you happen to have to make a possible IIG, this is done as soon as possible, with fewer risks to the mother.
Another indication of the the 2nd quarter screening is that being positive, and in the absence of chromosomal disorders this may indicate future obstetric problems, requiring greater vigilance of this pregnancy. We always advise as well, the realization of the 2nd quarter screening.
Integrated Screening
The integrated screening trace combines the 1st with the 2nd quarter and detects about 97% of cases (with about 3% false positives). This detection rate is similar to the 1st quarter screening with ultrasound conjunction.
Negative Prenatal Screening does not remove the possibility of your baby to have trisomy 21, 18, 13 or other abnormality of chromosomes or congenital. In most pregnancies, the risk is not increased and thus it is unlikely that the baby has Trisomy 21, 18, or 13. If these tests indicate an increased risk it does not mean that the baby has a problem, but that a diagnostic test should be made: amniocentesis.
What is Trisomy 21 or Down Syndrome?
The trisomy 21 is the most common cause of mental retardation in children. It affects one in 700 children in the world, in the absence of screening. The trisomy 21 is a genetic disorder caused by the presence of an excess of a chromosome 21 and is also known as Down syndrome or Mongolism. About half of children with trisomy 21 are carriers of heart malformations, digestive system, vision or hearing. The vast majority survives the first year and the average life expectancy exceeds 50 years. The risk of trisomy 21, very low in young women increases with age, particularly, over 35 years. However, most children with trisomy 21 are born to young women, because they are the ones that have more children. A child may be born with trisomy 21 even when there are no cases in the family. Usually the syndrome is not inherited.
What is trisomy 13 or Patau Syndrome?
Trisomy 13 is caused by the presence of a chromosome 13 in excess and affects about one in 12,500 to 21,000 pregnancies. In most cases, it is associated with increasing maternal age. It is also known as Patau Syndrome. The fetus with trisomy 13 has a sharp mental retardation, severe malformations of the central nervous system, heart, brain, kidney or eyes.
Most newborns die in the first month of life (80%) or in the first 6 months. Very few children reach adolescence and it is very rare to find adults with the Syndrome.
What is trisomy 18 or Edwards Syndrome?
Trisomy 18 is a rare chromosomal disorder that causes profound mental retardation and multiple congenital defects. Also known as Edwards Syndrome it is caused by the presence of a chromosome 18 in excess baby cells. About 1 in 8,000 babies are born with trisomy 18, and affects about twice as many female babies. Among other malformations are found, in patients with this disease: mental retardation, low birth weight, heart disease, malformations of the ears and hands, hernias and anomalies of the kidneys. Therefore, most children born with this syndrome do not survive the first year, and very few reach beyond childhood. As in the case of trisomy 21, the risk of having a fetus with trisomy 18 increases with maternal age.
What are Open Neural Tube Defects?
The Open Neural Tube Defects (NTDs) are congenital anomalies. There are two types: the so-called spina bifida, when the neural tube does not close completely during the first month of the embryo; and anencephaly, when the brain does not develop. In the absence of screening, about 1 in 2,000 babies is born with NTDs.
The vast majority (95%) appears in families with no previous history of NTD. Spina bifida can cause weakness or paralysis, loss of bladder control and in some cases mental retardation. The anencephaly causes fetal death hours or days postpartum.
