Are the results of Down syndrome screening accurate for irregular menstruation?

Pregnancy is a big event for every family. While eagerly looking forward to the arrival of a little life, every parent hopes to have a healthy baby. It is essential to go to the hospital for prenatal check-ups on time. The examination items at each stage of pregnancy are different. Among them, one of the important prenatal examinations is Down syndrome screening. Many people don't know much about Down syndrome screening.

Is the Down syndrome screening result accurate if the menstrual period is irregular?

Generally speaking, if the specific weeks of pregnancy are different from the weeks shown by B-ultrasound, most of the time the weeks of pregnancy shown by B-ultrasound should be used as the standard. Generally speaking, if the specific weeks of pregnancy are different from the weeks shown by B-ultrasound, most of the time the weeks of pregnancy shown by B-ultrasound should be used as the standard. Down syndrome screening is only a probability screening, not a diagnostic method. As long as the test is done between 16 and 20 weeks of pregnancy, the accuracy of the test results has nothing to do with the actual weeks of pregnancy, and the results are still accurate.

There are two main testing methods for Down syndrome screening:

1. Color Doppler ultrasound examination: The key examination item is NT, that is, the nuchal translucency, which is usually performed between 11 weeks and 13 weeks and 6 days during pregnancy. NT refers to the thickness of the fluid accumulated on the back side of the baby's neck when the baby is lying flat. The standard value is generally less than 3mm, and exceeding 3.5mm is considered abnormal. However, isolated NT thickening cannot be used to diagnose Down syndrome. It also depends on whether there are other abnormalities, such as nasal bone defects, other internal organ malformations, etc.

2. Blood test: It is usually carried out between 15 and 20 weeks of pregnancy. The best time for on-site sampling is between 15 and 18 weeks. The main test items are mainly four: alpha-fetoprotein (AFP), human chorionic gonadotropin (β-hCG), free estriol (uE3) and inhibin A.

Due to the existence of non-destructive testing technology and individual differences among inspectors, there is a possibility of missing screening. If the screening result is positive, the surface screening result is abnormal, and the pregnant woman has a high probability of having Down syndrome and is a key target, and further examination and diagnosis are required; if the screening result is negative, it means that the pregnant woman has a low probability of having Down syndrome and belongs to the low-risk group.

Once the blood test indicates that the baby is a key target, further amniocentesis will be required for diagnosis. Once diagnosed with Down syndrome, the pregnancy should be terminated immediately.

It should be noted that low risk does not mean zero risk, and there is still a possibility of missed screening, so it needs to be supplemented and confirmed by B-ultrasound examination results.