How do chromosome abnormalities happen?
Chromosomes are stick-shaped structures located in the center (nucleus) of each cell in the body. Each cell contains 46 chromosomes arranged in 23 pairs. An abnormal chromosome can create health concerns in the body. The most common cause of abnormal chromosomes is a mistake during cell division. Chromosome abnormalities are commonly caused by one or more of the following:
- Errors during the division of sex cells (meiosis).
- Errors during the division of additional cells (mitosis).
Other causes of birth abnormalities include exposure to a variety of substances (teratogens) in the developing fetus.
Errors during the division of sex cells (meiosis)
Meiosis (my-OH-sis) is the process by which sex cells split to produce new sex cells with half the amount of chromosomes. Sperm and eggs are sex cells. Meiosis marks the beginning of a baby’s development. Normally, meiosis results in each parent contributing 23 chromosomes to a pregnancy. When a sperm fertilizes an egg, the resulting infant has 46 chromosomes.
If meiosis does not occur properly, a baby may have an extra chromosome (trisomy) or a missing chromosome (monosomy). These issues can result in pregnancy loss or health complications for a child.
A woman aged 35 or older is more likely to have a baby with a chromosomal abnormality. This is because defects in meiosis may become more common as people age. All of the eggs in a woman’s ovaries are present from birth. The eggs begin to develop during adolescence. If a woman is 35 years old, her eggs are also 35. If you are pregnant and above the age of 35, you may be referred for genetic counseling or testing. Men produce fresh sperm on a continual basis. As a result, older dads are not more likely to have chromosome abnormalities. However, subsequent research indicates that uncommon irregularities do occur.
Errors during the division of additional cells (mitosis)
Mitosis (my-TOH-sis) refers to the division of all other cells in the body. It’s how a baby in the womb develops. Mitosis doubles the number of chromosomes to 92 before splitting them in half to return to 46. As the baby grows, this process occurs in its cells on a continuous basis. Mitosis continues throughout your life. It replaces damaged skin cells, blood cells, and other cells that die naturally.
During pregnancy, an error in mitosis may occur. If the chromosomes do not break into equal halves, the resultant cells may have an additional (47 total) or missing chromosome (45 total).
Risk of chromosome abnormalities by age
The chance of chromosomal abnormalities rises with maternal age. The likelihood of having a child with Down syndrome rises from about 1 in 1,250 for a woman who conceives at age 25, to around 1 in 100 for a woman who conceives at age 40. Many statistics only reflect live births and do not account for pregnancies with chromosomal abnormalities that were terminated or ended due to unplanned pregnancy loss, therefore the chances could be higher.
In general, having a child with Down syndrome increases the likelihood of having another with the condition. After age 40, the risk of recurrence for Down syndrome is determined by the mother’s age of delivery. It is crucial to note that the majority of newborns with Down syndrome are born to women under the age of 35. This is because women under the age of 35 have more children than women over 35. The doctor may recommend parents to a genetic specialist or genetic counselor who can go over the results of chromosomal tests in detail, including the chances of recurrence in future pregnancies and the tests available to discover chromosome issues before a baby is born.
Prenatal testing can help diagnose or rule out chromosomal abnormalities and other genetic birth issues. Blood tests, ultrasonography, testing of the tissues around the fetus, and amniocentesis are all possible methods of testing.
Risk of miscarriage with age
Some studies have found that elderly mothers are more likely to miscarry (lose their pregnancy early). When considering all women, approximately half of first-trimester losses are caused by a chromosomal defect in the fetus. Because these anomalies rise with the mother’s age, miscarriage is more likely. A new test is available that examines cell-free fetal DNA in the mother’s blood to detect chromosomal abnormalities.
While 35 is considered an advanced maternal age, risks rise as a woman ages. If you are pregnant and over the age of 30, consult your doctor about your personal health and make preparations to help you and your developing baby maintain a safe pregnancy.
Teratogens – substances that cause birth abnormalities
A teratogen (ter-AT-uh-jen) is something that can cause or contribute to a birth defect in a baby. They are items that a birth parent could be exposed to while pregnant. Teratogens include:
- Some medications
- Illegal drugs
- Alcohol
- Tobacco
- Toxic Chemicals
- Certain viruses and bacteria
- Certain forms of radiation
- Certain medical disorders, such as diabetes
Advanced age pregnancy guidelines
Obstetricians, the doctors who care for you during pregnancy and delivery, establish certain guidelines for advanced maternal age. Among these recommendations are:
- A daily low dose of prescribed medication to avoid preeclampsia if you have another risk factor in addition to your age.
- Discussing your options for prenatal genetic screening with your doctor.
- Doctors often point out that a C-section is unnecessary merely because you are older. Vaginal delivery can be safe. It is determined by your own health, the health of the child, as well as your own preferences.