Is it better to do non-invasive or Down syndrome test at 12 weeks of pregnancy? What tests should be done at 12 weeks of pregnancy?

We all know that after a woman becomes pregnant, she needs to go for regular prenatal checkups. There are many items in the prenatal checkups, and Down syndrome and non-invasive tests are the two most common and important ones. Most pregnant mothers need to do non-invasive tests and Down syndrome. So should we do Down syndrome or non-invasive tests at 12 weeks of pregnancy? Let's take a closer look!

What is Down's syndrome? What is non-invasive

Common Down syndrome screening test

The Down syndrome screening test done at 12 weeks is an early Down syndrome screening test, which includes hematological tests and ultrasound tests. The hematological test uses B-hcg and plasma protein A. The ultrasound part measures the fetal NT value (the thickness of the fetal nuchal translucency layer) for examination. The two test results are combined with the age of the pregnant woman and other conditions to infer the risk of fetal disease, with an accuracy rate of about 85-90%. In some areas, only early Down syndrome screening is recommended for young pregnant women with no adverse pregnancy and delivery history and other adverse factors. The cost of the test is also relatively cheap.

Non-invasive DNA test

Non-invasive DNA testing is a test that has become popular in recent years. Its biggest feature is its high accuracy rate. The overall accuracy rate is over 90%, especially for trisomy 21, the accuracy rate is over 99%. Its test uses a small amount of fetal DNA in the blood of pregnant women. The price is more expensive. Many netizens have left me messages saying that they can waive most of the fees or even provide free services in their places.

Is it better to have non-invasive surgery or Down syndrome at 12 weeks of pregnancy?

It is recommended to do the NT test first, and then choose Down syndrome screening or non-invasive screening according to your own situation.

NT and Down syndrome serum screening need to be done at 12 weeks of pregnancy. These two tests are recommended to be done between 11 and 13 (+6 days) weeks. Exceeding or earlier than this may lead to inaccurate results.

In fact, whether to do non-invasive or Down syndrome screening depends on the NT results and the pregnant mother's own condition. If the NT risk is high, non-invasive is recommended, and non-invasive is also recommended for older pregnant women.

The false positive rate of Down syndrome screening is high, and the accuracy rate is only 60~70%, but there are many screening items, while the non-invasive screening only screens the three common chromosomes, and the accuracy rate is as high as 99%.

However, it is worth noting that both Down syndrome screening and non-invasive screening are prenatal screening programs, not diagnostic results. No matter which one shows high risk, amniocentesis must be performed to confirm the diagnosis.

What tests should be done during the 12th week of pregnancy

Routine basic examination, blood routine, ABO blood type + Rh blood type, full biochemistry test (including fasting blood sugar, liver and kidney function), coagulation PT, coagulation APTT, coagulation Fib, urine routine, routine examination of vaginal secretions, bacterial vaginosis test (BV), five qualitative tests of hepatitis B, human immunodeficiency virus HIV, rapid syphilis serum reagin test, gonococcal smear staining, hepatitis C antibody determination, pregnancy thyroid function screening, LCT (liquid-based cell), Doppler fetal heart rate, obstetric ultrasound (10-14 weeks NT value), electrocardiogram.

Note:

① Go for the examination on an empty stomach;

② Several tubes of blood will be drawn on the day, so you should prepare some food in advance, especially sweets;

③ NT is a key examination item and may not be checked on the same day. In some places, an appointment must be made in advance, so it is best to make an appointment 12 weeks in advance.

Down syndrome and non-invasive testing time

NT, Down syndrome screening, and non-invasive testing can all screen for Down syndrome, but their examination time, examination method, and examination accuracy are all different.

1.NT examination

The best time to check is 11-13 weeks + 6 days of pregnancy. The thickness of the fetal nuchal translucency is checked by B-ultrasound to determine the possibility of fetal Down syndrome. Generally, if it is ≥3mm, the risk is relatively high and it is necessary to continue Down syndrome screening or non-invasive screening. The accuracy rate is 60-70%.

2. Down syndrome screening

The best time to check is 16-20 weeks of pregnancy. The risk of the fetus suffering from Down syndrome is calculated by drawing blood to test the values ​​of alpha-fetoprotein, human chorionic gonadotropin, free estriol and inhibin in the serum and then combining them with the age, gestational age and weight of the pregnant woman. The detection rate is 60%-70%.

Because the results of Down syndrome screening are greatly affected by age, it is not recommended for pregnant women aged ≥35 years to undergo Down syndrome screening, and they should go directly to non-invasive testing or amniocentesis.

3. Non-invasive DNA

The best time to check is 12-22 weeks + 6 days of pregnancy. It mainly takes venous blood from pregnant women for testing to determine whether the fetus is likely to have three major chromosomal diseases. The accuracy rate is as high as 99%.

Generally, pregnant women who fail the Down syndrome screening or are too old but do not want to do amniocentesis will choose non-invasive DNA. If the non-invasive DNA fails the test, amniocentesis can be done.