The difference between Down syndrome screening and amniocentesis

Down syndrome screening and amniocentesis are both common methods of pregnancy checkups. They have similarities, but also great differences. Generally speaking, amniocentesis is performed for some high-risk pregnant women, especially older mothers who have a greater chance of giving birth to a baby with Down syndrome, so amniocentesis should be performed in a timely manner. Down syndrome screening can be performed for most pregnant women.

The difference between Down syndrome screening and amniocentesis

NT

NT examination is one of the pregnancy check-up items, but many mothers do not know much about it. In fact, the NT test, also known as the nuchal translucency scan, is a method of assessing whether the fetus has Down syndrome, and it has a high accuracy rate.

What does the NT test check?

1. Fetuses with Down syndrome will have subcutaneous water accumulation, so the skin behind the neck will be thicker. If NT detects that the thickness of the fetal neck skin exceeds the standard value, it may be related to fetal chromosomal karyotype abnormalities and other structural malformations. The thicker the NT, the greater the probability of fetal structural abnormalities and chromosomal abnormalities.

2. In addition to the risk of detecting chromosomal abnormalities, thickening of the fetal nuchal translucency is also related to congenital heart disease.

If the NT test result exceeds the standard value range, pregnant women are advised to undergo follow-up fetal abnormality screening to further confirm the risk of fetal abnormalities so that timely countermeasures can be taken.

Down syndrome screening

Down syndrome screening is a method of predicting the risk of fetal malformation by extracting the pregnant mother's serum and testing the content of relevant proteins, hormones and other substances in it. It can be divided into early pregnancy Down syndrome screening and mid-pregnancy Down syndrome screening.

Early Down syndrome screening is usually performed between 11 and 13 weeks of pregnancy, and the judgment must be made based on the results of serum tests and NT values. The NT value refers to the thickness of the fetal nuchal translucency, which can be checked through B-ultrasound. The accuracy is relatively high, up to 90%.

Mid-term Down syndrome test time: 16-20 weeks; by extracting maternal serum, testing the concentration of alpha-fetoprotein and chorionic gonadotropin in the maternal serum, and combining the expected date of delivery, age, weight and gestational age of the pregnant woman at the time of blood sampling, the risk factor of giving birth to a Down syndrome baby is calculated. The accuracy is lower than that of the early Tang Dynasty, 60-70%.

A "high-risk" test result for an expectant mother only indicates that the probability of the fetus having Down syndrome is higher than 1/270, but it does not mean that the fetus will definitely have Down syndrome. So the next step is to further confirm whether the fetus is really a Down syndrome baby.

Sheep wear

The best time to do amniocentesis is between 16 and 20 weeks of gestation, usually for pregnant women aged 35 or above. During the procedure, a needle is inserted into your amniotic fluid under the guidance of a level 2 B-ultrasound to draw out some amniotic fluid, which is then taken out and placed in the laboratory for chromosome culture for about a week to determine whether the baby has any deformities, including cleft lip and congenital diseases. The gender can also be determined.

This experiment is risky, but the accuracy rate is over 99%. The best time to do an ultrasound is at 18 weeks, which can detect bone and visceral deformities including cleft lip, and can also determine the baby's gender.