Triple Screening: Pros And Cons, How It’s Done And When

When a woman becomes pregnant, she must undergo different evaluations to rule out future problems or malformations of the baby. One of these evaluations is the Triple Screening test, a test that is currently carried out as a routine test by the autonomous communities for free. Through screening tests, it is possible to have a statistical type value, which provides a sample of a risk . The information provided many times by the doctor, is expressed in a numerical value, which on certain occasions is a bit difficult to understand, especially for a pregnant woman who has no idea what the results of this test show.

In the modern world and with all the scientific advances related to embryonic medicine, you have at your disposal a lot of information regarding the factors that decrease or increase the risks of a specific pathology, in this way it is possible to have a more personalized risk . To cite an example, it is well known that the risk of chromosomal malformations in the embryo increases as the mother is older. But, by taking into account some important factors such as: blood levels of certain hormones or geographic markers, it is possible to jointly obtain a fairly reliable result, contrary to doing an isolated study of the age factor in the mother. Keep reading to clarify all the doubts related to this important test necessary in pregnancy.

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What is triple screening?

It is a filtering test which is performed on the pregnant woman to detect probable genetic alterations in the fetus. This test is carried out by means of a normal blood sample, it is not an invasive analysis in the future mother; which means that the triple screening does not imply any kind of danger for the fetus and neither for the mother . Triple screening or combined screening allows to measure the risk index of presenting chromosomal malformations in the fetus, such as Down syndrome, Trisomy 21, Edwards syndrome or Trisomy 18, etc. It is necessary to understand that triple screening does not provide a diagnosis as such, which means that it is not an unquestionable analysis.

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History of triple screening

The relationship between the risk of trisomies and maternal age was described in 1933, although it was not until the 1980s that the first triple screening tests were carried out. After different phases of scientific publications and research, the sensitivity of this type of test increased. The first was the screening carried out in the first quarter, whose sensitivity was between 65 and 70%. From the year 2000 to today, the screening or combined test has between 85 and 90% sensitivity; for which it has been adopted in hospitals by recommendations of scientific protocols.

Currently, most hospitals use the same software to calculate statistics and probability. In Spain, one of the centers that began the use of triple screening was the Hospital Clínico San Carlos in Madrid specifically, since mid-1999, a design based on the results obtained is used.

A logistic regression model is the statistical method used in this type of analysis . Regardless of the false negatives and false positives that occur in this method, it is possible to use these models as comprehensive tests by gynecologists and obstetricians. Today, triple screening is practically performed in almost all pregnancies because it is a reliable, earlier method and with fewer invasive analysis recommendations, where the mother’s age is a factor of less compromise when performing the risk calculation.

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Amniocentesis or triple screening? The same or different?

We already know that triple screening is a type of non-invasive test, on the other hand, we find Amniocentesis, which implies a significant risk of embryo loss (more or less between 1% and 2%), since It depends more on the woman’s overweight, if she has fibroids, if the placenta is located in the anterior face, the place of the baby and not on the person’s ability to perform Amniocentesis, that is, it is an invasive test.

In contrast, we have the triple screening which shows a high percentage of false positives and simply the probability of having Down syndrome is measured, Amniocentesis is responsible for diagnosing, in addition to this syndrome, other chromosomal diseases. It is essential that before undergoing triple screening or Amniocentesis, the opinion of the couple is taken into consideration and, based on the information obtained, the circumstances and their own values, define the convenience or not of the test.

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What is the theoretical discipline of triple screening?

Before developing this topic in depth, it is necessary that you understand that triple screening is simply a statistical test, none of the results obtained are considered as diagnostic, because there is a high probability of failure in the results. The statistical data can be obtained by means of 3 values ​​through analyzes carried out on the future mother in the revision consultation carried out in the 12th week of pregnancy: blood tests, ultrasound and data referring to the mother.

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How is a triple screening done?

By combining three biochemical markers found in the pregnant woman, the combined screening assessment is performed: alpha-fetoprotein produced by the fetus (PAPP-A), estrogen by the placenta and fetus (free estriol), in addition to the Chorionic Gonadotropin produced in the placenta (beta-HCG). The values ​​obtained from these biochemical markers are crossed with the information obtained by measuring the nuchal fold of the embryo, which is determined through an ultrasound and is approved taking into account the mother’s race, age, if she suffers from diabetes, its weight, among other variables. Finally, a control figure is obtained which will represent the probability of fetal abnormality.

The doctor may indicate other more specific tests, taking into account the results achieved, these tests can be a chorionic biopsy or amniocentesis. We can highlight that this test can detect between 75 and 85% of neural tube changes and 60% of Down syndrome, in women who do not reach 35 years of age. In contrast, in the group of women over 35 years of age, triple screening can detect 75% of cases of Down syndrome and neural tube singularities.

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Parameters

Triple screening is based on three parameters or pillars:

1. The mother’s age: it is essential to take into account the mother’s race or age, previous pathologies of the mother, addictions to alcohol or tobacco of the mother when evaluating the data and consider them when obtaining the statistical results .
2. Nuchal fold or translucency: nuchal translucency or fold and fetal length are assessed; according to the length measurements of the fetus, the nuchal fold data should be assessed. The fluid located and accumulated in the posterior area of ​​the fetus neck is measured through nuchal translucency (TN) ; All fetuses have this fluid, but sometimes this fluid increases. When the fluid is slightly increased it is not relevant, but it is necessary to observe the fetus and make other analyzes to define risks. An excessive increase in TN may signify some heart disease or chromosomal alteration, hence the importance of storing the data and carrying out diagnostic studies to clarify it.
3. Biochemical markers in the mother’s blood: This test will measure human chorionic gonadotropin, estriol, and alpha-fetoprotein. Estriol and hCG come from the placenta and the future baby, a measurement can be made by the mother. Alpha-fetoprotein is derived from the fetus and is found in maternal blood and amniotic fluid. When there are low levels of Estriol and AFP, in addition to high levels of hCG, the fetus can suffer from Down syndrome.

In order for you to better understand these parameters, it is necessary that you know that the three parameters have a moment during pregnancy, which serves to indicate the difference between children with Down syndrome and normal children, neural tube abnormalities or trisomy 18. In the In the case of a child with Down syndrome, beta hCG is high and PAPP-A is generally decreased. Similarly, a nuchal fold that exceeds 3 mm at this stage is a clear indication of risk. The valid time that is regular to the parameters goes from week 10 to week 12 + 3.

By mixing these three parameters, with the weight of the pregnant woman, her age and the time of pregnancy at which the samples are taken and the ultrasound is performed, the calculation of the possibility of a child being born with a chromosomal or tube alteration is made. neural. This does not mean that your baby has problems, it only shows a possibility that these problems are generated. On the one hand it contributes too many false positives, and on the other hand, it depends to a large extent on the moment in which the test is carried out, the laboratory and the person who performs the test. For the calculations through the computer to be complete, the tables in each center must be adjusted taking into account its population.

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goals

The main objective of triple screening is women with a low risk of having a fetus with chromosomal malformations. Similarly, women at high risk should also have this test: women whose previous pregnancies with chromosomal abnormality, women over 35 years of age, women with a family history of Down syndrome, women with previous pregnancies with congenital malformations without causes clear, women with repetitive abortions, as well as women exposed to elevations of ionizing radiation. The test is also carried out in future mothers at risk of being carriers of some chromosomal abnormality by the future father.

Levels and values

If you have received the results of your triple screening test, surely the values ​​and data expressed you cannot understand, this can cause you enormous confusion. Do not worry because we will try to explain in a simple way everything that is combined in the results obtained in your test, clarifying when they indicate some dangers of chromosomal alterations or when the values ​​in the fetus are normal.

The hormonal values ​​obtained by measuring the CRL, the PN and the age of the pregnant woman are entered into a computer program; after remixing you can predict the possibility of disturbances . The combination of these three factors and through the calculation carried out by the hospital center’s laboratory with a computer program, gives you a risk index. This shows you the possibility of the fetus acquiring a chromosome modification. The computer calculates the value and you can see it when you perform the ultrasound in the office in the 12th week of pregnancy. The values ​​that you can see in your triple screening are formulated in MoM.

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VALUES ​​CONSIDERED NORMAL

Values ​​between 0.5 and 2.5 MoM are considered normal. The different markers have a normal value of 1 MoM, the further the result is from 1 MoM, the more negative it will be. When the markers are in the following ranges, they can be considered suspicious:

• The plasma protein related to pregnancy (PAPP-A) is less than 0.4.
• Nuchal translucency (TN) is greater than 1.8 and up to 2.
• Human gonadotropin hormone (hCG or Beta hCG) is greater than 2.5 and less than 0.4.
• Alpha-fetoprotein (AFP) is greater than 2.5 or less than 0.4.
• The uE3 does not reach 0.5.
• Inhibin A is greater than 2.5.

After comparing these values, the most probable thing is that a chorionic biopsy or amniocentesis will be advised, both tests are invasive. In cases of risk of Trisomy 18 or Trisomy 21 with a lower value.

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Triple screening cut

This test establishes a cut-off point related to the risk of chromosomal variations. For Down Syndrome or Trisomy 21, the cut-off is located at 1: 270 (some laboratories may place it at 250), this means that a value that does not reach 270 can be considered as a high risk, but a higher value at 270 it can be considered low risk. For Edwards Syndrome or Trisomy 18, the cut-off point is located at 1: 100; which indicates that a value is considered high when it is less than 100, but a value greater than 100 is considered as low risk.

Results

The results of the triple screening test simply represent another statistic, under no circumstances are they considered a diagnosis. The statistics are largely conditioned by the age of the pregnant woman, the risk increases the older the woman; hence the importance of knowing the breakdown of the result in each case, since it is not the same that the result has been altered by the mother’s age than by the NT, because the future mother’s age only indicates that it is part of the statistical table and the TN gives true data of the fetus.

You must be calm if you obtained an unexpected result, remember that this test is not a diagnosis of anything and it speaks of 60% successes with high failures. When a high risk is identified and a reliable result is desired, an amniocentesis is necessary.

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Triple screening during pregnancy, are there risks? Which ones?

There is no risk in carrying out triple screening, since it is only a blood test that at no time can cause harm to you when you are pregnant and it cannot harm the fetus either. The bad thing that can happen is that it projects a result that causes you greater concern, until you can confirm that everything is fine and that it only represented an apparent alarm. Anyway, the best thing is to have a hard time and be foresight. It is a great way to ensure that your baby does not have any abnormalities, or if so, to make appropriate decisions. You can choose to carry out the test with the ultrasound in level II, if you do not want to suffer. If the results are normal, amniocentesis will not be necessary.

In addition, triple screening more than risks, gives you a great advantage compared to other kinds of tests, which does not include the risk of spontaneous abortion. Talk to your partner before undergoing the triple screening, it is essential that they talk about the decision to make if any abnormality is confirmed. By means of genetic tests you can have the necessary information to be prepared when your baby has an abnormality in its chromosomes, or in any case stop the pregnancy.

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First trimester

To calculate the risk of suffering a chromosomal alteration, especially Down syndrome, the gestational age, the mother’s age, analytical determinations, measurements of nuchal translucency are analyzed together. It is also necessary to consider other factors related to the pregnant woman: weight, race, if she is diabetic or smoker, the pregnancy is a twin or if the pregnancy was achieved by in vitro fertilization. It is possible to make some corrections that help to improve the precision when doing the risk calculation, but it will depend on each factor during the test.

Second trimester

Triple screening can also be done in your second trimester of pregnancy. Here your age is considered and the analytical values ​​are determined to be able to calculate the risk. At this time the test is less accurate than in the first trimester and the ultrasound parameter is not evaluated.

How does it affect a twin pregnancy?

If you have a twin pregnancy, you may have first trimester diagnostic tests, but with some peculiarities which allow us to conclude that triple screening in your first trimester of pregnancy has a slightly lower rate of Down syndrome compared to with a single pregnancy, than amniocentesis and chorion biopsy (invasive techniques), complication rates are higher than in a single pregnancy (because in a twin pregnancy, sample material must be taken from both placentas for biopsy and in the case of amniocentesis both bags must be punctured).

Furthermore, in maternal blood the reliability of the test is lower than in a single pregnancy.

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Difference between triple screening and combined test

Medical advances, studies and new technologies have made it easier for us to detect chromosomal abnormalities in fetuses from the beginning of gestation, in addition to using certain techniques that are not very invasive. You should not confuse these tests with diagnoses, they are simply statistical tests, which are based on biochemical markers present in measurements and in the future mother’s blood; establishing a risk relationship. On many occasions, the pregnant woman, because she has a high risk in these tests, has a very bad time and then it turns out that everything is normal. Now we will tell you about the difference between the combined test and the triple screening.

With respect to the combined test, this allows to detect anomalies in 90% which is carried out through the combination of pregnancy hormone (PAPP-A), nuchal translucency by ultrasound, free pregnancy hormone beta-hCG. Together with the crown-rump length (CRL) the data inform us about the risk of Edwards Syndrome and Down Syndrome through a computer program. This test is carried out between the 11th and 12th week of pregnancy, it is a fairly sensitive technique. It is possible that you have not been able to perform this test due to some complication such as not having your pregnancy checked early. It is at this time that you have another option: triple screening.

When the pregnancy is more advanced (around week 14), it is possible to apply another kind of test whose reliability is more or less than 75%, that is, its reliability is lower than that of the previous test. This test, as we said before, measures the chorionic gonadotropin hormone, nuchal translucency of the baby through ultrasound and the measurement is made in the blood test of the protein associated with pregnancy (PAPP-A). Together with the weight of the pregnant woman, the age and time of the pregnancy at which the samples are taken and the ultrasound is performed, it is possible to make the calculation of having a child with some chromosomal alteration.

Currently the combined test has been replaced by the combined screening or first trimester test, thanks to its high sensitivity .

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Pros and cons of triple screening

When you are pregnant, it is normal for doubts about maternal tests to recur. One of these doubts focuses on the advantages or disadvantages of the triple screening or first trimester test. Here we clarify what the pros and cons of this test are, so that you can enjoy this wonderful stage in your life with more peace of mind.

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Pros of triple screening

• Triple screening is an inexpensive test.
• It is very useful, since it gives you enough information about the risk of suffering an alteration, without the need to undergo an invasive test such as amniocentesis, which includes certain risks.
• This test is simple to perform.
• You can get the results in just one week.
• It does not involve any type of risk.
• It performs an important filtering of pregnant women, which are at risk or not.
• The triple screening is carried out in the first trimester in parallel with the analytical one.

Cons of triple screening

• It is an indicative test, it is not a definitive diagnosis.
• By having a false positive result, you can take the risk of having an amniocentesis, assuming the probable risks.
• It can be an unnecessary concern due to a false positive (this represents one of the most common disadvantages of this test).

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When is a triple screening performed? Why?

Triple screening is performed between week 10 and week 13 of pregnancy, the most reliable result of this test can be obtained between week 11 and 12, its diagnostic sensitivity is between 86% and 90% , with just 5% false positives.

In some cases, triple screening is carried out when the second trimester of gestation begins (weeks 15 and 18 of pregnancy), although ideally it should be between weeks 16 of gestation and 15. Even this test can be performed in week 20, but it barely has a diagnostic sensitivity of 78%, but the false positives are 14%. At this stage of pregnancy, it is more likely that an invasive test such as amniocentesis will be considered, if this is your case, you are in the legal stage to voluntarily interrupt your pregnancy or continue the pregnancy, but take the appropriate precautions .

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Triple screening vs Harmony

The Harmony test, unlike triple screening, which is a conventional non-invasive maternal test, allows detecting common chromosomal abnormalities by measuring the number of chromosomes in maternal blood. Harmony is a test that can possibly displace the chorionic biopsy or amniocentesis, one of its advantages is that it is earlier and is not invasive, avoiding the risks involved in the extraction or puncture of a substance or tissue sample. Although triple screening is a test with similar results, Harmony is considered one of the most accurate and reliable prenatal tests, recommended by recognized specialists, and is further supported by the Fetal Medicine Foundation in London.

The most frequent trisomies that can be detected by the Harmony test are: Trisomy 13 (Patau Syndrome), Trisomy 18 (Edwards Syndrome), Trisomy 21 (Down Syndrome), in addition to other less frequent syndromes such as Klinefelter Syndrome or Turner Syndrome. From week 10 on, any pregnant woman can take the Harmony test. Even this test can be performed in twin pregnancies, in vitro fertilization by receiving eggs.

To take the Harmony test, only a normal blood sample is drawn. Currently this test does not replace the other invasive methods and neither does it displace non-invasive tests such as the triple screening test; it is only performed in private gynecologist consultations or in private clinics. If you are interested, you should only consult with your gynecologist about the probability of doing this test.

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Egg donation and triple screening

If you are one of the women who has resorted to embryo or egg donation, you probably have doubts about triple screening and egg donation. As you already know, egg donation is the reproduction treatment that women choose when they have exhausted all possibilities of getting pregnant, it is a difficult decision since you had to give up your genetics . The fetus will only have the genetic part of the father and the rest of the genetics is owned by the anonymous donor.

But it is necessary to remember that Trisomy 21 (Down syndrome) can occur in a mother of any age, although the percentages in these cases are quite low. Triple screening allows an analysis based on the combination of several parameters with an ultrasound, together with the age of the anonymous donor, they provide percentages as a result that indicate the possibility that the future baby will acquire Down Syndrome. When the percentages have alterations or the results obtained in the ultrasound, the doctor will recommend an invasive test (amniocentesis). Only both parents as a couple, must make an important decision about it.

Gynecologists when advising the performance or not of amniocentesis are quite prudent, since in both decisions there is a certain risk, it is you who must balance the consequences of the decision to be made.

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Importance of triple screening nuchal translucency

When speaking of nuchal translucency, we refer to the fluid accumulated in the nape and posterior area of ​​the neck of the embryo, under the dermis. Through an ultrasound, this fluid can easily be measured, between week 11 and week 14 of gestation. So your gynecologist will perform a measurement through ultrasound at week 12 of pregnancy. Today it is known that fetuses with Trisomy 21 or other trisomies, the nuchal translucency has a greater thickness. For this reason, the translucency or nuchal fold represents one of the essential bases of triple screening or prenatal screening carried out during the first trimester of pregnancy.

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Triple screening in Down syndrome

If you had a triple positive screen, you are probably thinking that Down syndrome is safe in the fetus. This is not true, the result simply speaks of the possible risk and they conclude on the cases that have a certain high risk to need another test, but invasive such as amniocentesis or chorionic biopsy. In this test, the chromosomes of the fetus are subjected to studies to rule out or confirm a certain alteration at that height.

That is, if the risk of the triple test exceeds 1: 300, it is essential to perform amniocentesis or chorionic biopsy. Previously, all future mothers over 35 years of age were offered it, but today this has been left aside, thanks to the high accuracy when performing the screening tests.

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Importance of triple screening

During pregnancy, most women undergo prenatal diagnostic processes in order to ensure the proper development of the pregnancy and the viability of the fetus. Although there are some detractors in this regard, since they point out that these diagnostic techniques are simply a selective method of people. We consider this idea to be wrong, since making a prenatal diagnosis is more beneficial, especially if you carry a fetus with a trisomy and you will surely appreciate all the information received that will help you properly prepare for the care of the future baby and for delivery.

When we refer to prenatal diagnosis, this includes: the company of the preconception doctor, who goes through the pregnancy until after delivery. Along with the controls of blood pressure, weight, blood, glucose and diet during pregnancy; the doctor uses some techniques available to verify the proper development of the embryo. All this requires individualized monitoring of each pregnancy.

Many babies thanks to these techniques are helped to be born healthy, because it is possible to detect malformations or abnormalities that can be corrected immediately after delivery or during pregnancy . It is also possible to reveal family-transmitted diseases and birth defects, as well as determinants of the type of delivery. One of the non-invasive techniques that exist is the triple screening test after the ultrasound performed in the 12th week of pregnancy to make the risk calculation for Trisomy 21 and in this way the most convenient decision can be made or a further diagnosis can be chosen . certain through an invasive test.

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Does a low-risk combined screening rule out Down syndrome?

Triple screening tests cannot totally rule out the existence of chromosomal diseases, they simply support parents when deciding to carry out other extra genetic analyzes. Some babies with chromosomal abnormalities or later in the last trimester of pregnancy can be identified on ultrasound done in the second trimester. Only a small percentage of pregnant women can have a fetus with trisomy that was previously not suspected in the screening tests.

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Does increased nuchal translucency invariably indicate that the baby has Down syndrome?

Not necessarily, 80% of fetuses with Trisomy 21 have an increased nuchal translucency. In many cases of fetuses with Edwards Syndrome, Patau Syndrome, and Turner Syndrome at 11 and 13 weeks have increased nuchal translucency, usually along with other important factors. However, at least 20% of fetuses have a chromosomal disease. There are other reasons why the fetus may have increased nuchal translucency: skeletal dysplasias, heart disease and rarely in cases of infections, severe anemia in the fetus and other rare genetic conditions . A significant number of fetuses with increased nuchal translucency are healthy. For this reason, it is that nuchal translucency should not be considered as a pathology but as another risk factor.

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What to do if I don’t make it to the first trimester screening?

Performing the screening test during the first trimester of pregnancy is essential at this stage due to its simplicity and high reliability, it is possible that you are one of the few patients who have not been able to perform the test for different reasons, which may include: knowledge late pregnancy. If this were your case and you are already in the 14th week of pregnancy, it is possible to perform another test whose reliability is acceptable, although the detection rate is 75%.

The triple screening test in the second trimester of pregnancy calculates the risk for the following trisomies: 13, 18 and 21 based on the inherent risk due to the age of the mother transformed by the deviation of biochemical annotators of the second trimester of gestation. The mother undergoes an analysis between week 14 and week 20 of pregnancy. The most effective test is the quadruple test which includes: alpha-fetoprotein, the beta portion of hCG, inhibin A, and unconjugated estriol; expressing its result as risk, being adjusted for the mother’s particularities (race, age, weight, etc.). If it is equal to or greater than 1: 250, it is considered high risk for trisomies 18, 13 or 21. With regard to multiple pregnancies, the detection rate is less effective with only 50%.

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Cases in which an invasive procedure is indicated

After performing a triple screening test in the first trimester of pregnancy, the following criteria are considered to indicate an invasive procedure:

• If there is evidence of fetal malformation which was detected in the first trimester through ultrasound.
• When the test reports a risk greater than 1: 250 for trisomies 18, 21, and 13.
• If in any of the parents there was an anomaly.
• If an abnormality was detected in a previous pregnancy.

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