Second trimester antenatal screening

In modern society, prenatal check-ups are commonplace for pregnant women. It is a manifestation of responsibility towards the fetus and themselves. Prenatal check-ups can monitor the health of both in real time and rule out some special situations. In the second trimester of pregnancy, which is between 18 and 24 weeks, the prenatal check-up that needs to be done is to screen for possible congenital diseases and malformations in the fetus. The following terms are most likely to appear on the check list.

1. What does AFP mean?

AFP is a fetal-specific globulin, also known as serum alpha-fetoprotein. It is a special protein contained in the human blood during the embryonic period. It may have the immunoregulatory function of glycoprotein during pregnancy and can prevent the fetus from being rejected by the mother.

2. How to understand Free HCG and what does MOM mean?

HCG is human chorionic gonadotropin synthesized by placental cells and is composed of two subunits, a- and b-. HCG enters the maternal blood after fertilization and proliferates rapidly until the 8th week of pregnancy, then slowly decreases in concentration until the 18th to 20th week, and then remains stable. HCG can be used for early pregnancy testing, ectopic pregnancy, incomplete abortion, etc.

The MOM value is the ratio of the marker detection value in the woman's body to the median of normal pregnant women at the same gestational age. Because the levels of prenatal screening substances change cyclically with gestational age, the MOM value needs to be standardized to facilitate clinical judgment.

3. About trisomy 21, 18, and 13

A normal human body has 23 pairs of chromosomes. Trisomy 21, 18, and 13 means that the fetus has one more chromosome in the 21st, 18th, and 13th pairs than normal. Trisomy 21 is Down syndrome.

In this regard, the international standard is 1/270. When the blood test screening value is greater than 1/270, it is a high-risk group. The normal value is around 1/700. Currently, the most accurate way to determine whether a fetus has Down syndrome is amniocentesis, which involves extracting amniotic fluid, culturing the cells shed by the fetus in the amniotic fluid, and testing the fetus's 21 chromosomes. However, amniocentesis does have certain risks.