Chromosomes

Chromosomes and Pregnancy

Each cell in our body contains chromosomes. Chromosomes contain DNA which determines our genetic makeup. Each cell contains 46 chromosomes, made up of 23 individual pairs – one pair comes from the mother and one pair comes from the father.

Most babies will have normal chromosomes, but we know that sometimes chromosome problems can occur. This is called “aneuploidy”. Changes in the number, structure and arrangement of chromosomes is determined at conception and cannot be altered. There may be fewer chromosomes than normal or more chromosomes than normal. There can be parts of chromosomes missing (called “deletions”) or rearranged (called “translocations”). Changes in the chromosomes are usually significant and can cause miscarriage or birth defects.

First trimester screening assesses the risk for your baby having the following chromosome abnormalities:

• Trisomy 21 (also known as Down syndrome)

These babies have an extra chromosome 21 in each cell of the body. Down syndrome is one of the most common chromosome abnormalities, affecting 1 in 600 live births. It is associated with intellectual delay and physical problems such as heart and intestinal defects.

• Trisomy 18 (also known as Edward syndrome)

These babies have an extra chromosome 18 in each cell of the body. Trisomy 18 is associated with multiple and severe birth defects. Babies with this condition usually die during the pregnancy or shortly after birth.

• Trisomy 13 (also known as Patau syndrome)

These babies have an extra chromosome 13 in each cell of the body. Trisomy 13 is associated with multiple and severe birth defects. Babies with this condition usually die during the pregnancy or shortly after birth.