Second trimester Screening test

The screening of the second trimester of pregnancy includes the following:
•    Quadruple Test
•    Contingent Test
•    Neural tube defects screening (NTDs Screening Test)

Quadruple Test:

This screening is performed from the beginning of the 15th week of pregnancy (15W+0D) to the end of the 22nd week of pregnancy (22W+6D) when the head diameter (BPD) is in the range of 21 to 57 mm. In this screening, the risk of two common chromosomal abnormalities including Down's syndrome (trisomy 21), Edward's syndrome (trisomy 18), and neural cord disorders (NTDs) in the fetus is calculated. Depending on the type of abnormality and the age of the mother, this screening has a predictive ability of 56-76% and is performed by measuring the amount of four hormones Inhibin-A, AFP, uE3, and Total-hCG in the mother's blood.
Laboratory indicators used in second-trimester screening

1. AFP (alpha photoprotein): It is a protein that is produced during pregnancy first by the yolk sac and then by the liver of the fetus. During pregnancy, this protein enters the mother's blood and amniotic fluid. The amount of this substance in the mother's serum increases until the 30th week of pregnancy and after that, it starts to decrease. In pregnancy with a fetus with Down syndrome, its amount decreases, and with the ural tube and abdominal wall defects, its amount increases. In congenital abnormalities, twin pregnancy, fetal loss, placental disorders and problems, pre-eclampsia, premature birth, and low birth weight, this protein can be increased in the mother's blood.
2. Total- hCG (human chorionic gonadotropin): hCG is the first measurable hormone related to pregnancy. This hormone is first produced by the trophoblast and then by the placenta. In the first weeks of pregnancy, its concentration doubles almost daily, and it reaches its maximum level in the 10th to 12th weeks of pregnancy, and it decreases until the 18th week of pregnancy, and then its level remains almost constant. In pregnancy with a fetus with Down syndrome, its amount increases, and in trisomy 18 it decreases.
3. uE3 (unconjugated estriol): This substance is made in the placenta, liver, and adrenal glands of the fetus. The amount of free estriol increases until late pregnancy. This substance decreases in pregnancy with a fetus with Down syndrome and trisomy 18.
4. Inhibin A: It is a glycoprotein secreted by the placenta. Its level reaches a constant level in weeks 15 to 20 of pregnancy and then increases with a very low slope until the end of pregnancy. The amount of this substance increases in pregnancy with a fetus with Down syndrome. It should be noted that all the above laboratory indicators increase with the increase in the number of embryos.

The screening results of Down syndrome and trisomy 18 with the quad test are presented as follows:
High-risk group (Screen Positive): genetic counseling is recommended to decide to perform cell-free fetal DNA or amniocentesis diagnostic tests. (high risk in screening does not mean a definite infection)
Low-risk group: continuation of usual pregnancy care is recommended.
The screening results for nerve cord disorders or NTDs with the quad test are presented as follows:
High-risk group (Screen Positive): Specialist counseling and targeted ultrasound are recommended.
Low-risk group: It is recommended to continue the usual pregnancy care under the supervision of the relevant gynecologist.

Contingent Test (combined test):

If the patient has done his first-trimester screening at the same institution, a combined final risk will be reported by combining the risk of the first trimester and the risk of the second trimester. In this screening, the risk of three common chromosomal abnormalities including Down's syndrome (trisomy 21), Edward's syndrome (trisomy 18), and Pato's syndrome (trisomy 13) is calculated in the fetus. The accuracy of this screening is almost 95%.
Contingent Test screening results are presented in one of the following two ways:

• High-risk group (Screen Positive): Specialist genetic counseling and amniocentesis diagnostic test are recommended (high risk in screening does not mean a definite diagnosis).
• Low-risk group: It is recommended to continue the usual pregnancy care under the supervision of the relevant gynecologist

Neural tube defects screening (NTDs Screening Test):

Screening for nerve cord disorders (NTDs) is done using ultrasound or AFP measurement or both. The concentration of alpha photoprotein (AFP) can be measured in maternal blood and amniotic fluid. This screening can be done by measuring AFP in the mother's blood from the beginning of the 15th week of pregnancy (15W+0D) to the end of the 22nd week of pregnancy (22W+6D). Nerve cord disorders are caused by neural tube closure disorder during a fetal period with involvement of the bones around the developing nerve cord. Neural tube disorders include spina bifida and anencephaly, although the appearance of these two disorders is different, both are considered manifestations of the same disorder.

The accuracy of screening by measuring the concentration of AFP in the mother's blood is 76% for open spina bifida and 85% for anencephaly.

In measuring the amount of alpha-photoprotein, gestational age, several fetuses, mother's weight, race, and insulin-dependent diabetes are considered.

In the screening of nerve cord disorders by measuring AFP in the mother's blood, the concentration of this protein in a pregnant person is compared with the median obtained in other pregnant women with healthy fetuses at the same gestational age in the same center (MoM). Screening is done using this number. (It should be mentioned that the obtained number of alpha phytoprotein (MOM) is related to the technology used, the software used, and the number of tests and screening performed at the test site).
Screening results of nerve cord disorders using From AFP of mother's blood:
High-risk group (Screen Positive): genetic counseling and targeted ultrasound are recommended.
Low-risk group: It is recommended to continue the usual pregnancy care under the supervision of the relevant gynecologist.
HopeGene Medical Institute is the only center that can measure amniotic fluid alpha photoprotein (AFP) concentration in those undergoing amniocentesis for any reason.
If the amniotic fluid alpha-phytoprotein concentration increases, amniotic fluid acetylcholinesterase is measured. If amniotic fluid acetylcholinesterase is positive even though ultrasound findings are normal, the diagnosis of neural tube disorders (NTDs) is confirmed.
Other causes of amniotic fluid alpha-phytoprotein (AF-AFP) concentration, except for NTDs, include: fetal death, open ventral wall defects such as gastroschisis, embolus, Turner syndrome, and congenital kidney disorders.