The amniotic fluid was normal but a baby with Down syndrome was born

We all know that pregnant women have to undergo Down syndrome screening during pregnancy. If the Down syndrome screening shows a low risk value, they will be required to undergo further examination, which is the so-called amniocentesis. Amniocentesis can more directly determine whether the baby is well developed or whether he or she has Down syndrome. Because the probability of amniocentesis is much higher than that of Down syndrome screening, it is more credible, but nothing is completely absolute. So how can a baby with Down syndrome be born when the amniocentesis is normal?

Amniocentesis is a test to diagnose whether the fetus has chromosomal abnormalities. If the amniocentesis result shows that the fetus has trisomy 21, will the child be born normal? The final result of amniocentesis showed that the fetus has trisomy 21, with an accuracy rate of 99%. The child born is abnormal and has congenital idiocy. Trisomy 21, also known as Down syndrome, is a disease caused by gene abnormality. The chromosome 21 of the child changes from the normal 2 to 3. It is also one of the most common birth defects in my country.

The incidence of Down syndrome is related to the mother's age during pregnancy. It is an abnormality of chromosome 21 and has three types: trisomy, translocation and mosaicism. Older pregnant women and aging eggs are important causes of non-disjunction. Most fetuses with Down syndrome will die before birth. If they are born in time, most children will have severe intellectual disabilities and other problems, such as leukemia, gastrointestinal malformations, etc. They are unable to take care of themselves and have a short lifespan, with an average survival age of only 20-30 years old and an IQ generally between 20-50.

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 accuracy of Down syndrome screening is about 70%, and it is usually performed between 15 and 20 weeks of pregnancy. The best time to do a level 2 B-ultrasound is at 18 weeks, as it can detect skeletal and visceral deformities including cleft lip, and can also determine the baby’s gender.

Pregnant women over 34 years old; those with a family history of Down syndrome; those with a high probability of Down syndrome in the maternal blood, i.e. greater than 1/270; those with abnormal nuchal translucency; those with abnormal ultrasound examination.