Down Syndrome (Trisomy 21)

Every cell in the body normally contains 46 chromosomes, arranged in 23 pairs, which carry our genetic instructions. In Down syndrome there are three copies of chromosome 21 instead of two — hence the name Trisomy 21. This extra genetic material changes the way the brain and body develop.

• Learning & development: All children with Down syndrome have some degree of learning disability, but this varies widely. Many go to mainstream school with support, form friendships, and become semi-independent adults.
• Physical features: Common features include a characteristic facial appearance, low muscle tone (hypotonia) in early life, and a single crease across the palm — although none of these is present in every child.
• How it happens: In most cases the extra chromosome arises by chance during the formation of the egg or sperm, or in early cell division. It is not caused by anything the parents did before or during pregnancy.

Down syndrome can occur in any pregnancy, but some factors raise the chance:

• Maternal age: The single biggest factor. The chance rises gradually with age — roughly 1 in 1,500 at age 20, about 1 in 900 at 30, around 1 in 350 at 35, and approximately 1 in 100 by age 40. That said, because more babies are born to younger mothers overall, the majority of babies with Down syndrome are born to women under 35.
• A previous affected pregnancy: This modestly increases the chance in a future pregnancy.
• Translocation carriers: In a small minority (about 3–4%) the trisomy is caused by a translocation, where chromosome 21 material is attached to another chromosome. One parent may carry this in a balanced form, which is why we offer parental testing and genetic counselling when translocation Down syndrome is diagnosed.

It is important to separate screening (estimating the chance) from diagnosis (a definite answer).

Screening tests (safe, no risk to the pregnancy):

• NIPT (Non-Invasive Prenatal Testing): A maternal blood test from 10 weeks that analyses cell-free placental DNA. It is the most accurate screening test for Trisomy 21, detecting over 99% of affected pregnancies with a very low false-positive rate.
• Combined test: Performed at 11–14 weeks, it combines the nuchal translucency (fluid at the back of the baby's neck) with maternal age and two blood markers to produce a risk figure.

Diagnostic tests (give a definitive answer, small procedure-related miscarriage risk):

• CVS (Chorionic Villus Sampling): From 11 weeks, samples the placenta.
• Amniocentesis: From 15 weeks, samples the amniotic fluid.
• The sample is analysed by karyotype (a picture of all the chromosomes) or chromosomal microarray, which confirms Trisomy 21 and identifies the underlying mechanism (standard trisomy, translocation, or mosaicism).

A positive screening result should always be confirmed with a diagnostic test before any irreversible decisions are made.

When Down syndrome is suspected or confirmed, our care focuses on information and preparation rather than treatment of the pregnancy itself.

• Detailed anomaly scan: We perform a careful fetal heart scan (fetal echocardiography) and a detailed structural survey, because Down syndrome is associated with specific findings.
• Associated findings to look for: Around 40–50% of babies have a congenital heart defect (most often an atrioventricular septal defect). Some have duodenal atresia (a blockage of the upper bowel, seen as a 'double bubble' on scan), and there may be soft markers such as a small or absent nasal bone.
• Non-directive counselling: We explain what the diagnosis means, what to expect, and all available options in a balanced way — without steering you toward any particular choice. Families are given time, written information, and access to support groups and, where wished, meetings with paediatric specialists.
• Planning for birth: If the pregnancy continues, we arrange delivery in a unit with neonatal and, if a heart defect is present, paediatric cardiology support.

The outlook for children with Down syndrome has improved dramatically and continues to do so.

• Life expectancy now commonly reaches the late 50s and 60s, largely because heart defects can be surgically repaired in infancy with excellent results.
• Development: Children reach the usual milestones but often later, and benefit greatly from early intervention, speech and physiotherapy, and inclusive education.
• Quality of life: Most people with Down syndrome and their families report a positive quality of life, and many live semi-independently, work, and take part fully in their communities.
• Health follow-up: Lifelong monitoring is recommended for thyroid function, hearing and vision, and certain other conditions that are more common, so that they can be treated early.

Referral to the MFM Unit is appropriate when:

• A screening test (NIPT or combined test) shows an increased chance of Trisomy 21.
• The nuchal translucency is increased, or the anomaly scan shows a heart defect, duodenal atresia, or several soft markers.
• There is a family history of Down syndrome or a known chromosomal translocation.
• Parents simply wish to discuss their options and have a diagnostic test.

At the MFM Unit, Dr. Ali Al Ibrahim and the fetal medicine and clinical genetics team provide screening, diagnostic testing, detailed scanning, and unhurried, non-directive counselling at our centres in Abu Dhabi and Al Ain, coordinating with paediatric cardiology and neonatology where needed.