How many times should Down syndrome screening be done?

Checkups during pregnancy are very important. Not only do you need to do blood and urine tests, but you also need to check for progesterone, progesterone, and various other tests that pregnant women need to do. After a certain period of time, you also need to measure your abdominal circumference to see if the baby's growth and development is within normal standards. Some families consider genetic diseases and do Down syndrome screening as soon as they become pregnant. How many times does this screening need to be done?

Screening process

First trimester

This examination mainly uses two screening methods, "ultrasound" and "blood test", when the pregnant mother is between 10 and 13+6 weeks of pregnancy. Dr. Huang Xuguang said that ultrasound can clearly measure the thickness of the fetal nuchal translucency, and blood tests can be used to measure the plasma protein A value and human chorionic gonadotropin value in the mother's serum to estimate the risk of the fetus suffering from Down syndrome.

Second Trimester

When pregnant mothers have their blood drawn at 15 to 20 weeks, the hospital will test the serum levels of alpha-fetoprotein, human chorionic gonadotropin, free estriol and inhibin, and then calculate the risk of the fetus suffering from Down syndrome based on the mother's age, weeks of pregnancy and weight.

Chorionic villus sampling

Dr. Huang Xuguang said that pregnant mothers must discuss this test carefully with their doctors first because it is an invasive test that requires obtaining some cell samples from the developing placenta. He gave an example that when a pregnant mother undergoes first trimester screening, if the fetal nuchal translucency is more than 3 mm, she can consider doing chorionic villus sampling directly to test the chromosomes. However, the results of this will not be known until 14 days later.

Amniocentesis

This is also an invasive test but carries fewer risks than chorionic villus sampling. Dr. Huang Xuguang said that by extracting amniotic fluid from the amniotic cavity of the pregnant mother's uterus for testing, it can be determined whether the fetus's chromosomes are abnormal and whether the fetus is likely to have Down syndrome. It takes 14 days to get the results and its accuracy is over 99%.

Development History

Before 1984, amniocentesis was performed on pregnant women aged 35 years or older to examine the chromosomes of amniotic fluid cells.

In 1984, Dr. Merkatz, Dr. Cuckle & Wald of the United States found that the AFP level in the blood of pregnant women with Down syndrome was about 15% lower than that of normal pregnant women.

In 1987, Dr. Bogart found that the blood levels of β-hCG in pregnant women with Down syndrome were higher than those in normal pregnant women.

In 1988, Canick, Haddow, and Wald found that the blood levels of pregnant women with Down syndrome were decreased. At the same time, the Triple Test, a triple screening program for Down syndrome, was proposed for the first time.

In 1996, inhibin A became the fourth serological test indicator and the quad test for Down syndrome was proposed.