What is the normal value of NT test for pregnant women? What are the reasons for high nt values?

NT is one of the important indicators for pregnant women's examination and plays an important role in indicating whether the fetus is developing well. The normal range of the nt value is 2.5mm and below. If it exceeds this range, the fetus may have symptoms such as Down syndrome or congenital diaphragmatic hernia. In addition, Down syndrome screening is also a way to check whether the fetus has Down syndrome. Below we will introduce the normal range of NT values, the causes of abnormalities, and the difference between NT values ​​and Down syndrome screening!

1. Normal values ​​of NT examination

1. The normal value of NT examination: less than or equal to 2.5mm.

2. Abnormal NT examination: greater than or equal to 2.5mm.

2. Reasons for high NT value

1. During normal embryonic development, the cervical lymphatic vessels and the jugular sinus are connected at around 11-14 weeks. Before the communication, a small amount of lymph fluid accumulates in the neck, causing temporary NT thickening. In a normal fetus, the disease should disappear after 14 weeks. However, if the connection between the cervical lymphatic vessels and the cervical venous sinuses is delayed, resulting in obvious cervical lymphatic reflux disorder, excessive accumulation of lymph fluid in the neck, obvious thickening of the NT, and even development into cystic hygroma in the second trimester.

2. Fetuses with normal chromosomal karyotype but congenital heart malformations often have increased NT, which may be related to heart failure. When heart failure occurs, venous return is impaired, resulting in increased jugular venous pressure, obstruction of lymph return in the lymphatic vessels, and excessive accumulation of lymph in the neck, forming NT thickening.

3. The extracellular hyaline matrix of the neck skin of fetuses with Down syndrome increases, and the extracellular fluid is adsorbed in large quantities in the intervals of the hyaline matrix, causing spongy changes in the neck skin and forming NT thickening.

4. Congenital diaphragmatic hernia: due to the herniation of abdominal contents into the chest cavity, the intrathoracic pressure increases; space-occupying lesions in one lung cause the volume of the lung on that side to increase, resulting in mediastinal shift and venous return obstruction; fatal skeletal deformities, extremely narrow chest cavity, and increased intrathoracic pressure can all lead to venous return obstruction and venous congestion. When venous blood flows back to the neck and head, the NT thickens.

3. The difference between NT examination and Down syndrome screening

1. NT screening refers to the thickness of the nuchal translucency and the serum test of pregnant women. The nuchal translucency refers to the space where water accumulates under the skin behind the fetus' neck. During an ultrasound scan, the doctor will measure the thickness of the space between the skin and tissue in detail. The nuchal translucency will be significantly thickened in fetuses with chromosomal abnormalities, especially in babies with Down syndrome. Down syndrome is usually more likely to occur in older mothers. Medical literature has confirmed that the thicker the nuchal translucency of the fetus, the higher the chance of chromosomal abnormalities. NT screening is performed between 11 and 13 weeks of pregnancy.

2. Down syndrome screening is a detection method that extracts serum from pregnant women, tests the concentration of alpha-fetoprotein, chorionic gonadotropin and free estriol in the maternal serum, and calculates the risk of giving birth to a fetus with congenital defects based on the pregnant woman's expected date of delivery, weight, age, weight and gestational age at the time of blood collection. The best time to do Down syndrome screening is between 15 and 20 weeks of pregnancy.