How to detect Down syndrome in a baby: signs and symptoms

In this article, we address a topic that often concerns new parents: at what age can Down syndrome be recognised in a baby? Detection of trisomy 21 (Down syndrome) can take place before or after birth. It is therefore important to become familiar with certain characteristic signs and symptoms so that a doctor can be consulted promptly if necessary.

Trisomy 21: what is it?

Trisomy 21, also known as Down syndrome, is a genetic condition characterised by the presence of an extra chromosome on pair 21. In other words, instead of the usual 46 chromosomes, the affected individual has 47. This genetic anomaly leads to various health problems that can vary in severity from one person to another. It is therefore essential to detect trisomy 21 as early as possible in order to support the affected child and allow for their optimal development.

Prenatal detection of trisomy 21

Currently, several tests are available to screen for trisomy 21 during pregnancy. These tests consist of various combinations of ultrasound scans and blood tests carried out at different stages of pregnancy. Prenatal screening methods are generally safe for both mother and child, but they are not always entirely reliable.

First-trimester combined screening

This screening is carried out between the 11th and 14th week of pregnancy, allowing the risks of trisomy 21 to be assessed. It combines two examinations: an ultrasound scan and a blood test. The ultrasound measures the nuchal translucency (the distance between the skin and the soft tissue at the back of the neck), while the blood test determines the levels of two markers present in the maternal blood: PAPP-A (a placenta-related indicator) and beta-hCG (the human chorionic gonadotropin hormone).

The cell-free DNA test in maternal blood (NIPT)

The NIPT is a non-invasive test that can be performed from the 12th week of pregnancy and analyses foetal DNA present in the maternal blood to detect the presence of the extra chromosome 21.
It offers very high sensitivity for screening trisomy 21, with a detection rate of over 99%, but it remains a screening test rather than a diagnostic one.

Prenatal diagnostic tests

When the result of a screening test indicates a high risk of trisomy 21, further examinations may be offered to reach a definitive diagnosis. These examinations are invasive and carry risks for the foetus. They consist of amniocentesis (sampling of amniotic fluid) or a chorionic villus biopsy (sampling of a portion of the placenta).

Postnatal detection of trisomy 21

Even though prenatal tests are available, they are not always used, or their accuracy may be limited in certain cases. It is therefore important to know the signs that may suggest trisomy 21 in a newborn.

Physical characteristics

A baby living with trisomy 21 may present several distinctive signs, although they are not always present or pronounced. Here are a few:

Low muscle tone and general hypotonia (an unexplained "floppiness")

Slightly almond-shaped eyes, angled upwards and with a small fold of skin covering the inner corner (the well-known epicanthal fold)

A wider gap between the first and second toes

A single palmar crease running across the palm of the hand instead of the usual two curves (known as the single transverse palmar crease)

Development and behaviour

Children with trisomy 21 generally show delays in their overall development, particularly in terms of language, motor skills and independence. These delays can become apparent from the first few months of life. Some babies may also have difficulty feeding or regulating their body temperature.

When trisomy 21 is suspected: consulting a doctor

If you are concerned about clinical signs suggesting trisomy 21 in your baby, it is important to consult a healthcare professional promptly. Screening is carried out using an examination called a karyotype, which allows the number of chromosomes present in the child's cells to be observed.

In summary, trisomy 21 can be detected before and after birth through various prenatal tests and observable symptoms in the newborn. It is essential for parents and doctors to work together in order to detect this anomaly quickly and provide appropriate support.