Aneuploidy

What are chromosomes?

Humans have chromosomes, which are thread-like structures inside the nucleus of each cell. Chromosomes carry DNA that surround proteins like a tight spring. DNA is your body’s instruction manual that your biological parents pass down to you. Your DNA is what makes you unique. You’ll receive 23 chromosomes from each of your biological parents (46 total). These chromosomes are arranged into pairs; we inherit one chromosome of each numbered pair of chromosomes (1 through 22) from each parent; and then genetic males inherit and X and a Y, while genetic females inherit two X chromosomes.

Cells have a short lifespan and they constantly need to be replaced. Cell division happens when new cells replace old cells, similar to how you would use “copy and paste” on your computer. During this process, DNA distributes evenly throughout new cells when the chromosome pairs in the old cell separate from each other, then copy themselves. This happens throughout our lives but also in the creation of egg and sperm cells. Sometimes, chromosomes aren’t divided equally, causing the number of a specific chromosome someone has to be inaccurate. This can lead to a genetic condition diagnosis like Turner syndrome or Down syndrome.

What is aneuploidy?

Aneuploidy occurs when the number of chromosomes a cell has doesn’t equal 46. While this can happen sometime during your lifetime, more often, it occurs when the number of chromosomes your child acquires from their biological parents doesn’t equal 46 due to an error in the creation of the egg or sperm. There can be an extra copy of a chromosome (trisomy) or a missing copy of a chromosome (monosomy), making the total number of chromosomes not a multiple of 23.

Changes in the number of chromosomes from each biological parent can affect the outcome of a pregnancy, most often resulting in a miscarriage. Studies show that aneuploidy affects almost half of pregnancies that end in a miscarriage in the first trimester.

What are the types of aneuploidy?

There are two main types of aneuploidy; there can be an extra copy of a chromosome (trisomy) or a missing copy of a chromosome (monosomy). Humans have 23 pairs of chromosomes, totaling 46 chromosomes. A person with an aneuploidy condition typically has either one more or one less chromosome than normal.

Trisomy

Trisomy occurs when a person has an extra copy of a chromosome. A baby with trisomy has 47 chromosomes. Common conditions that are the result of trisomy include:

• Down syndrome: An extra copy of chromosome 21.
• Trisomy 18:An extra copy of chromosome 18 that used to be called Edwards syndrome.
• Trisomy 13: An extra copy of chromosome 13 that used to be called Patau syndrome.

Monosomy

Monosomy occurs when a person is missing a copy of a chromosome. Their total chromosome count equals 45. A common condition that’s the result of monosomy is Turner syndrome.

A sex chromosome determines your baby’s sex identity assigned at birth. There are two sex chromosomes, X and Y (XX for female and XY for male). A Turner syndrome diagnosis, or monosomy X, occurs when your baby only has one X sex chromosome instead of a pair.

Who does aneuploidy affect?

Fetal aneuploidy can affect any baby. The risk of having a child with fetal aneuploidy is higher among individuals who have a higher maternal age (with the exception of Turner syndrome). For example, at 20 years of age, your risk of having a child with a chromosome abnormality is 1 out of every 1,480 pregnancies. At age 40, your risk is higher, estimating 1 out of every 65 pregnancies for having a child with a chromosome abnormality.

If you’re planning on becoming pregnant, talk with a healthcare provider about genetic counseling to screen for potential genetic conditions.

How common is aneuploidy?

Fetal aneuploidy and chromosome disorders affect about 1 out of every 150 pregnancies and are responsible for about 50% of early pregnancy losses.

How will trisomies and monosomies affect my pregnancy?

Having an extra copy of a chromosome (trisomy) or missing a copy of a chromosome (monosomy) can affect the outcome of a pregnancy.

Trisomies most often result in a miscarriage. Studies show that trisomies cause an estimated 35% of all miscarriages. Although rare, around 1% of trisomies result in a live birth, most often trisomy 21, or Down syndrome. If your baby is born with a trisomy condition, their survival rate could be lower than normal due to defects that your baby has at birth (congenital defects).

Monosomies are less common than trisomies and only one variation of monosomy X, also known as Turner syndrome, results in a live birth. Turner syndrome occurs when only one X chromosome is complete. The absence of a Y chromosome is responsible for assigning babies as female at birth.

What are the symptoms of aneuploidy?

The most common symptom of aneuploidy is a miscarriage, which is when a pregnancy ends early. A miscarriage will usually occur during the first three months of pregnancy but can happen at any time. Symptoms of a miscarriage include:

• Abdominal pain and lower backaches.
• Cramps.
• Light to heavy bleeding.

If you think you’re having a miscarriage, contact your healthcare provider immediately.

Although 50% of pregnancy losses are due to genetic abnormalities like aneuploidy, it’s possible to have a baby born with an aneuploidy diagnosis. Babies with aneuploidy are much more likely to have birth defects and are much more likely to face developmental delays and intellectual disabilities.

What causes aneuploidy?

Aneuploidy is the result of a genetic error that most often happens before the fertilization of sperm and egg cells. Cells divide to make more cells. This process, also known as meiosis, occurs when a single cell (with 46 chromosomes) divides twice to create two cells (gametes) with half of the original amount of their genetic code (23 chromosomes). These gametes form your body’s sex cells, which are sperm in males and eggs in females. Aneuploidy occurs during meiosis when pairs of chromosomes don’t complete the process of cell division and fail to separate.

Aneuploidy is random and unpredictable. Similar to how your office printer might malfunction, you never know when the copying mistake will arise in your DNA. To understand your risk of having a child with a genetic condition, talk with your healthcare provider about genetic counseling.

How is aneuploidy diagnosed?

Three tests can diagnose fetal aneuploidy during pregnancy, including:

• Chorionic villus sampling (CVS): In the first trimester, between 10 and 13 weeks, CVS checks for aneuploidy and sometimes other genetic conditions. Your healthcare provider will take a small sample of cells from your placenta to test them for genetic conditions.
• Amniocentesis: Amniocentesis checks for aneuploidy and sometimes other genetic conditions and a few congenital defects. It’s done starting at 15 weeks but typically by 20 weeks of pregnancy. Your healthcare provider will take a small sample of your amniotic fluid to test for a variety of health conditions.
• Noninvasive prenatal testing: Noninvasive prenatal testing, also known as noninvasive prenatal screening or aneuploidy screening, occurs after 10 weeks of pregnancy when your healthcare provider will draw a sample of blood from your vein to assess whether or not your baby is at increased risk of having an aneuploidy condition.

How is aneuploidy treated?

Most aneuploidies are fatal for your baby and/or cause birth defects like intellectual disability or multiple medical problems that need individualized treatment plans to keep them healthy.

People who are pregnant are at risk of a miscarriage due to aneuploidy. A number of people who experience a miscarriage have subsequent normal pregnancies and births. If you face a miscarriage, you may need time to heal both physically and emotionally from the loss.

If you’re looking to expand your family by becoming pregnant, talk with your healthcare provider about genetic testing and ways that you can improve your chances of having a successful pregnancy.

How can I reduce my risk of having a child with aneuploidy?

You can’t prevent aneuploidy from occurring. But you can reduce the risk of having a baby with birth defects by:

• Eating a well-balanced diet.
• Getting genetic screenings done before you plan on becoming pregnant.
• Not smoking or drinking alcohol.
• Taking prenatal vitamins.

If I miscarry as a result of aneuploidy, can I become pregnant again?

It’s possible to have a healthy pregnancy after a miscarriage. Aneuploidy miscarriages are the result of a genetic mutation that’s spontaneous and unpredictable. The risk of having a baby with an aneuploidy diagnosis following an aneuploidy miscarriage is low in most instances. Discuss the risks of genetic disorders with your healthcare provider before you decide to become pregnant.

What can I expect if I have a child with aneuploidy?

Most often, parents will face a miscarriage after an aneuploidy diagnosis. This is a very difficult experience and is the result of a genetic mutation during fertilization, not something that the parent did while pregnant. Your healthcare provider will recommend ways you can heal both physically and emotionally after a miscarriage.

If you have a child after an aneuploidy diagnosis, they’ll be at risk of developmental delays in their lifetime, including short stature, congenital defects and intellectual disabilities. Make sure you stay regular with wellness checkups with your healthcare provider to address any side effects that may arise as a result of an aneuploidy diagnosis. There isn’t a cure for aneuploidy.

When should I see my healthcare provider?

If you’re experiencing symptoms of a miscarriage, contact your healthcare provider immediately and they’ll let you know whether or not you should visit the emergency room.

After a miscarriage, if you experience any of the following symptoms, contact your healthcare provider immediately because you might have an infection:

• Chills.
• Fever.
• Heavy bleeding.
• Pain and discomfort.

What questions should I ask my doctor?

• Am I at risk of having a child with a genetic disorder?
• Is my body healthy enough to have a child after experiencing a miscarriage caused by aneuploidy?
• Do you recommend additional prenatal screenings if I’m at risk of having a child with a genetic disorder?

What is the difference between aneuploidy and polyploidy?

Aneuploidy and polyploidy are both genetic disorders that refer to a change in the number of chromosomes in your baby’s DNA. The difference between the two conditions is that aneuploidy is an extra or missing chromosome, or in rare cases, a couple extra/missing chromosomes. Polyploidy describes a person who inherited extra set(s) of 23 chromosomes from a parent — for instance, inheriting 46 chromosomes from one parent and 23 from the other (triploidy).

A note from Cleveland Clinic

When you’re using a copier in your office, sometimes, the machine will spontaneously print a page that’s askew or the machine will stop working temporarily, most often due to a paper jam. Similar to genetic conditions, spontaneous changes occur within your DNA that can lead to an aneuploidy diagnosis. You can’t prevent genetic conditions, but your child can live a happy and healthy life with their diagnosis. If you plan on becoming pregnant, talk with your healthcare provider about genetic counseling to assess your risk of having a child with aneuploidy and to reduce your risk of miscarriage.