Second Trimester Screening or Quad Marker

  Second Trimester Screening or Quad Marker 



In 1866, Dr. John Langdon Down published an article in the United Kingdom in which children with common characteristics were spoken of and their IQ was lower than that of normal children. Dr. Dawn named the group of children because of their resemblance to the Mongol people, Mongol. But years later, in the early 1960s, the name was removed from all scientific texts due to protests by Asian geneticists, and the disorder has since been called Down Syndrome. In 1930, scientists discovered that Down syndrome was caused by a genetic disorder.


Down syndrome is known to be the most common genetic disorder [3] (with a prevalence of 1.5 cases per 1,000 live births). A percentage of fetuses with Down syndrome die before the mothers give birth.



Due to the relatively high prevalence of Down syndrome, various methods have been developed over the past 10 years to diagnose this dangerous disease before birth [4]. However, for various reasons, such as the risk of miscarriage and the high cost of testing, it is not possible for all pregnant women to perform these procedures. For this reason, in recent years, screening methods have been developed to identify pregnant women who are most at risk, and these individuals are considered eligible for diagnostic procedures [5].



The incidence of Down syndrome is directly related to maternal age, so that the risk of giving birth to infants with Down syndrome in mothers up to the age of 30 is almost constant and is about 1 in 1,000, and then increases exponentially. So that at the age of 35 it becomes 1 in 250 and at the age of 40 it becomes 1 in 75. However, 80% of Down syndrome cases occur in women under the age of 35 (because the number of pregnancies at this age is much higher).



Women who have had Down syndrome in previous pregnancies are also at higher risk. The influence of other factors such as father's age, history of infection in second or third degree relatives, environmental radiation, etc. has not yet been fully proven.



One of the most common and reliable screening methods in the second trimester of pregnancy is the Quadraple Marker test, or CWA Marker test for short, which involves measuring several pregnancy products in the mother's blood and comparing the values ​​obtained with the normal values ​​of the community. .



Quad Marker's test is more accurate than its predecessor, the triple marker test, and its false positives are less accurate, and today it has replaced the triple marker test.



This test can be performed technically from the beginning of week 14 (0D + 14W) to the end of week 22 (22W + 6D) of pregnancy and the best time to perform the test in Iran is week 15 of pregnancy (and in other countries from 15W + 2D to 17W + 0D ) Is.

The probability of Down syndrome is calculated by performing statistical calculations on the values ​​obtained from the test, maternal age and other factors such as maternal weight, smoking history, diabetes, twin pregnancies and so on. Special software is designed for this purpose, which shows the risk of fetal infection in numbers as well as specific curves.

Ultrasound findings also help determine the risk of fetal Down syndrome. The most common ultrasound scan in my lower extremity is to increase the thickness of the folds behind the fetal neck. Quad Marker's test results also indicate the risk of two other congenital diseases. These diseases include trisomy 18 and neural tube defects.



Markers measured in the second trimester

Alpha-Proteoprotein (AFP): Alpha-Proteoprotein is an albumin-like protein that is synthesized first in the yolk sac and then in the liver of the fetus. Some of the alpha-protein synthesized enters the mother's bloodstream through the placenta (after crossing the blood-placental barrier) and in very small amounts through the amniotic fluid. The dose increases until the end of the second trimester of pregnancy (weeks 14 to 20) and then decreases, giving way to albumin. In pregnancy, the effects of fetuses with Down syndrome are reduced, and in the opening of the neural tube and abdominal wall, the amount is higher than expected.

In addition, an increase in AFP in twin pregnancies, fetal loss, placental disorders including bleeding (especially in mothers who have spotting from the beginning of pregnancy), chorioangioma, chorionic villitis, and any placental vascular disorders that cause further shedding. AFP is seen by the fetus in the mother's blood, as well.

An unexplained and unexplained increase in this marker (AFP MoM> 2.5) is associated with an increase in pregnancy complications such as placental hemorrhage, oligohydramnios amenorrhea, fetal death (Intra Uterine Fetal Death = IUFD), gestational hypertension, and preterm delivery.

Single declines in this marker (AFP MoM> 0.25) have also been associated with increased incidence of miscarriage, stillbirth, preterm delivery, and macrosomia.



Human chorionic gonadotropin (hCG): HCG is the first measurable product of pregnancy, and in the first weeks of pregnancy its concentration doubles almost daily, reaching about 100,000 mIU / ml in 10 to 12 weeks, and then to the end of pregnancy. It decreases to about 10,000 mIU / ml in the third trimester of pregnancy.

The hormone is first synthesized from the corpus luteum and then from the placental cytofibroblast cells.

It has two subunits, alpha and beta, whose beta component is specific to this glycoprotein hormone, while its alpha component is similar to that of other glycoprotein hormones (TSH, FSH, and LH).

Various studies have shown that fetal blood hCG is important in the development of adrenal and fetal glands in the second trimester of pregnancy. As this hormone causes the corpus luteum to survive (to continue producing progesterone).

HCG measurement in the second trimester has a higher diagnostic value than free beta hCG for Down syndrome.

An over-expected increase in this marker could indicate choriocarcinoma, mole hydatid form, or multiple pregnancies. In vascular disorders and placental hypoxia, proliferation (proliferation) of placental trophoblast cells can be seen, resulting in increased hCG production.

An increase in the unexplained cause of this marker (hCG moM> 3.0) is associated with increased complications such as preeclampsia, preterm delivery, IUGR, and stillbirth.

 In the blood of a pregnant woman, we see 5 different forms of hCG-dependent molecules or hCG-related molecules:

- nonnicked hCG, which represents the active hormone;

There is a peptide bond in the beta chain of hCG to which the steroidogenic or steroidogenic activity of the hCG molecule depends.

- nicked hCG;

- free α-subunit;

- free β-subunit;

- and the nicked free β subunit



Non-conjugated estriol (uE3):
The dihydroepiandrosterone sulphate (DHEA-SO4) produced in the fetal adrenal gland in the liver is hydroxylated and then metabolized in the placenta to non-conjugated sterols and enters the mother's bloodstream.

Its half-life in maternal blood is 20 to 30 minutes, and it is conjugated to glucuronide in the mother's liver and excreted by the kidneys. Free estriol levels increase during pregnancy and peak during childbirth. It is used as an indicator in determining the time of delivery because it has a sudden increase approximately 4 weeks before delivery.

Since all uE3 in the mother's blood is of fetal origin, it can be used as an indicator of chromosomal abnormalities.

In Down syndrome and trisomy 18, the rate of this marker decreases. In cases such as Smith-Lemley-Opitz syndrome (SLOS), deficiency of the aromatase enzyme, disorders of the contiguous gene syndrome, and the primary and secondary defects of the fetal adrenal gland, uE3 levels are reduced.

Its increase is seen in congenital adrenal hyperplasia (CAH).

The unexplained decrease in this marker (uE3 MoM> 0.5) was associated with an increase in pregnancy complications such as oligohydramnios, fetal death over 24 weeks (IUFD), and intrauterine growth retardation (IUGR).



Marker DIA) Inhibin A):
 Inhibin molecules are dimeric glycoproteins that have two alpha and beta chains. The alpha chain in all subscribers and the existence of beta A or beta B chain causes the name Inhibin A or Inhibin B.

The Inhibin A marker is secreted from the ovaries and placenta and is secreted mainly from the placenta as the gestational age increases, especially in the third trimester.

Its levels increase in the first trimester of pregnancy, decrease in the second trimester, and then increase again in the third trimester.

Its physiological effect on pregnancy is unclear, but its increase or decrease is highly consistent with hCG, and the causes of hCG increase also increase DIA.

In fetuses with Down syndrome, an increase in hCG and Inhibin A levels and a decrease in AFP and uE3 levels are seen.

Individual and unexplained increases in this marker (DIA MoM> 2.0) are associated with increased blood pressure, gestational proteinuria, and other pregnancy complications such as IUGR.



Maternal follow-up protocol in second trimester screening

According to the results of the Down syndrome screening test in the second trimester, mothers fall into four groups:

1- High risk group: If the risk of the fetus is more than 1: 250 (or the number 1: 270 according to the national procedure), after confirming the age of the fetus, the mother will be referred for genetic counseling and amniocentesis. . If the fetal age differs from the reported age by more than 7 days in response to the test, the mother will be referred to a laboratory to recalculate the risk. If LMP (the first day of the last menstrual period) is used to determine the age of the fetus, an ultrasound must be performed before performing amniocentesis to confirm the age of the fetus.

Note 1: If the risk to the fetus is only positive for trisomy 18 because the trisomy is associated with IUGR [1] (which is intrauterine growth retardation), the age difference between ultrasound and LMP is worthless.

Note 2: If the amniocentesis response is normal, these women should be included in the high-risk group in terms of adverse pregnancy outcomes and increased prenatal care for them (including scanning anomalies in weeks 18-18, 24-week pregnancy ultrasound for rejection). IUGR, control of blood pressure, control of urinary protein excretion, control of vaginal discharge to rule out infection, etc.).

2- Borderline risk group: If the risk of Down syndrome is between 1: 800-1: 250, a detailed ultrasound is recommended at 20-18 weeks.

However, the NIPT test can also be recommended to this group, and this test can be used as a preferred suggestion.

Also the presence of abnormal levels of markers such as:

- (AFP (MoM ≥2.5

- (hCG (MoM .3.0

- (Inhibin A (MoM .3.0

- (uE3 (MoM .0.4

Increases the likelihood of adverse pregnancy outcomes, increases the need for prenatal care.

3- Low risk group: low risk less than 1: 800. In this case, the screening for Down syndrome ends.

4 - If the result of screening for nerve cord disorders is more than the risk of segregation (1: 100), scanning anomalies can be used with more focus on the neural tube, placenta and abdominal wall (for information on the risk of neurological disorders) (See AFP).

According to the latest BCPGSP guidelines, a detailed ultrasound of the second trimester at 18-18 weeks should be recommended for all pregnant women. If there is no Down syndrome marker in this ultrasound as mild marker [2], trisomy 21 risk can be considered reduced by up to 50%.]

 
Tip 1: Wherever there is talk of screening, we will definitely have false positives and negatives, and all scientific and legal centers will accept it. For example, in the quad marker test, when we say that it has a detection power of 80%, it means that it is able to detect 80 cases of Down syndrome out of 100 cases, and those 20 cases that cannot be diagnosed are considered as false negatives.


[1]. (IntraUterine Growth Restriction (= IUGR

[2]. soft markers


[3]. The cause of Down syndrome in 95% of cases is the absence of chromosome 21 during meiosis cell division, which occurs in 90% of cases in the ovum. Excess chromosome 21 in Down syndrome causes overactive genes involved and eventually overproduction of certain proteins that cause the symptoms of Down syndrome.

[4]. These include amniocentesis (the acquisition of embryonic cells and their chromosomal examination).

[5]. The difference between screening and diagnostic methods is that in a diagnostic test, a positive result means the definite existence of a specific disease or condition; But in a screening test, the goal is to assess the risk of disease or a specific condition. So a positive result shows an increase in risk. Unlike screening methods, diagnostic methods are usually costly, time consuming, and sometimes risky, but have more accurate results.

[6]. Quad Marker