Understanding Down syndrome and the importance of prenatal screening

The arrival of a new life should be a joyous occasion, but the older the expectant mother, the higher the chance of giving birth to a baby with Down syndrome. Down syndrome can affect a person's physical characteristics, vital signs, health, learning patterns, and many other aspects of their life; it is an incurable disease. However, expectant mothers can undergo Down syndrome screening tests during pregnancy to predict the likelihood of their fetus having Down syndrome.

What is Down syndrome?

Down syndrome is a genetic disorder caused by a chromosomal abnormality. Normal chromosomes come in pairs; most human cells carry 23 pairs of chromosomes, which govern traits such as appearance, skin color, and intelligence. Nearly 95% of people with Down syndrome have an extra chromosome (trisomy 21), causing slower growth and potentially resulting in delayed brain and limb development. Most children with Down syndrome have mild to moderate intellectual disability, with an IQ similar to that of an 8- or 9-year-old child. They may also experience complications such as congenital heart defects, skeletal abnormalities, and vision or hearing impairments.

What are the characteristics of people with Down syndrome?

In fact, Down syndrome varies in severity, but because babies with Down syndrome develop more slowly in terms of both physical and psychological development, they generally exhibit the following physical characteristics:

• The head shape, face, and nose are flat and small;
• Eyes tilted upwards;
• The ears are abnormally shaped and positioned too low.
• Fine mouth;
• The tongue is large and textured, and some may protrude outside the mouth;
• Short neck;
• Short, stubby fingers;
• Weak muscle tone;
• Short in stature;
• The second phalanx is underdeveloped;
• There is a noticeable gap between the big toe and the second toe on the foot;

• obese

In addition, people with Down syndrome are very likely to have one or more other conditions, such as: congenital heart disease, hearing loss, deafness, myopia, strabismus, lacrimal duct obstruction, cataracts, otitis media, pneumonia, sleep apnea, intestinal obstruction, joint dysplasia, myeloproliferative disorders, etc.

Causes of Down syndrome

Regardless of gender, if a person has Down syndrome, their offspring will inevitably inherit the Down syndrome gene. However, the vast majority of Down syndrome cases are accidental. The older the pregnant woman, the greater the uncertainty regarding chromosome division in her egg, thus increasing the risk of her fetus having Down syndrome. As for the pregnant woman's lifestyle habits before or during pregnancy, current research has not indicated a direct relationship between these habits and the fetus having Down syndrome.

Down syndrome prevention screening

Preconception testing can calculate and predict the probability of a baby having Down syndrome without causing any harm to the pregnant woman or the fetus. The screening methods for Down syndrome vary depending on the stage of pregnancy.

• Early pregnancy screening & mid-pregnancy screening :

	Early pregnancy screening	Mid-pregnancy screening
Inspection Items & Contents	"Nuchal measurement": Measuring the thickness of the fetal nuchal translucency using ultrasound. Blood test: Testing for pregnancy-associated plasma protein A (PAPP-A) and human chorionic gonadotropin (hCG) levels.	Blood test: to check levels of alpha-fetoprotein (AFP), human chorionic gonadotropin (hCG), estriol, and inhibin-A.
Inspection period	11 to 14 weeks of pregnancy	16 to 20 weeks of pregnancy

If the screening results in the early or mid-pregnancy period are positive, a second-stage diagnostic test is required: chorionic villus sampling (CVS) between 11 and 14 weeks of pregnancy, or amniocentesis between 16 and 20 weeks of pregnancy. The principle is to use a fine needle inserted into the uterine cavity under ultrasound guidance to extract placental villi or amniotic fluid for chromosome analysis. However, it is important to note that the risk of miscarriage increases by 0.8% after undergoing this second-stage diagnostic test.

• Non-invasive prenatal testing for fetal chromosomal abnormalities:

To accurately assess the chances of a fetus having Down syndrome or to avoid increasing the risk of miscarriage due to invasive testing, pregnant women may consider choosing the non-invasive fetal chromosomal aneuploidy detection technology "NIPD Zplus test".

	NIPD Zplus detection
Inspection Items & Contents	DNA extraction and analysis: 10 mm of peripheral blood was extracted from the pregnant woman, and cell-free fetal genes were extracted and analyzed using bioinformatics sequencing technology.
Inspection period	10 weeks or more of pregnancy
Suitable for	Pregnant women aged 35 or older; twin pregnancies; recurrent miscarriages; high-risk pregnancies identified by serum screening; and women undergoing in vitro fertilization (IVF).

Renhe Medical Examination Centre in Hong Kong offers prenatal screening for Down syndrome. A single test can determine the probability of the fetus having chromosomal abnormalities such as T21 Down syndrome, T13 Patau syndrome, and T18 Edwards syndrome. Other tests include blood tests, urine tests, ultrasound, gestational diabetes screening, and HIV testing. Please inquire for more details or book your test now .

Disclaimer: This content is independently written by a third party and is provided for informational purposes only. It is not sponsored in any way, cannot replace professional medical advice, diagnosis, and treatment, and does not represent any position. If you experience any discomfort, it is recommended that you seek medical attention as soon as possible.