Trisomy 13 and trisomy 18 are genetic problems. They involve a combination of different birth defects. These include severe learning problems and health problems that affect nearly every organ in the body.

Most babies born with trisomy 13 or 18 die by age 1. But some babies with these problems do survive the first year of life. It's hard to predict how long a child with these problems might live. There are some reports of babies with trisomy 13 or 18 surviving to their teens.

Chromosomes come in sets of two, or pairs. Most people have 23 pairs of chromosomes in their cells (46 chromosomes total). Trisomy means that a person has three copies of a certain chromosome instead of two. Trisomy 13 means the child has three copies of chromosome number 13. Trisomy 18 means the child has three copies of chromosome number 18.

A normal egg cell and normal sperm cell start with 46 chromosomes. The egg and sperm cells then divide their chromosomes by half. The egg and sperm cells then have 23 chromosomes each. When a sperm with 23 chromosomes fertilizes an egg with 23 chromosomes, the baby will then have a complete set of 46 chromosomes. Half are from each birth parent.

But sometimes an error occurs when the 46 chromosomes are being divided by half. An egg or sperm cell may keep both copies of chromosome number 13 or 18, instead of just one copy. If this egg is fertilized or if this sperm fertilizes an egg, then the baby will have three copies of chromosome number 13 or 18. If the baby has three copies of chromosome number 13, this is called trisomy 13. If the baby has three copies of chromosome number 18, this is called trisomy 18. The extra copy of chromosome number 13 or number 18 is present in every cell in the body.

Sometimes the extra number 13 or number 18 chromosome, or part of it, is attached to another chromosome. This is called a translocation. This is the only form of trisomy 13 or 18 that may be inherited from a birth parent.

A rare form is called mosaic trisomy 13 or 18. This is when an error in cell division happens after fertilization. People with this syndrome have some cells with a typical number of chromosomes and some cells with an extra chromosome number 13 or 18.

Symptoms can occur differently in each child.

A baby with trisomy 13 may have symptoms such as:

• Low birth weight.
• Small head with sloping forehead.
• Structural problems of the brain, such as the front of the brain not divided normally (holoprosencephaly).
• Eyes that are close together.
• Nose or nostrils not well developed.
• Cleft lip and cleft palate.
• Small jaw.
• Low-set ears that have an abnormal shape.
• Scalp problems that look like sores (cutis aplasia).
• Purplish-red birthmarks from tiny blood vessels close to the skin (hemangiomas).
• Extra fingers and toes (polydactyly).
• Feet with prominent heels.
• Short neck.
• Heart defects.
• Kidney problems.
• Part of the belly (abdominal) organs bulging through an opening near the umbilical cord (omphalocele).
• In male babies, testes not descended into the scrotum.
• In female babies, a uterus that forms in two branches (bicornuate uterus).

A baby with trisomy 18 may have symptoms such as:

• Looking thin and frail.
• Failure to thrive.
• Problems feeding.
• Small size, even when delivered at full term.
• Small head.
• Low-set ears.
• Small mouth and jaw.
• Shortened breastbone (sternum).
• Small pelvis.
• Weak cry.
• Problems with hearing.
• Heart defects.
• Can't extend fingers fully.
• Arms and legs in a bent position (contracture).
• Feet with a curved shape under the heel, known as rocker bottom.
• Spinal cord not fully closed (spina bifida).
• Eye problems.
• Cleft lip and palate.
• Slow growth.
• Seizures.
• High blood pressure.
• Kidney problems.
• Curvature of the spine (scoliosis).
• In male babies, testes not descended into the scrotum.

Most babies with trisomy 18 have problems that affect all parts of the body. Heart problems, feeding problems, and infections are what most often lead to death.

Chromosome problems, such as trisomy 13 or 18, can often be diagnosed before birth. This is done by looking at cells in the amniotic fluid or from the placenta (called chorionic villous sampling). This can also be done by looking at the amount of the baby's DNA in your blood. This is called noninvasive prenatal screening and can be done on those of any age during pregnancy. These tests are very accurate.

Fetal ultrasound during pregnancy can also show the possibility of trisomy 13 or 18. But ultrasound is not 100% accurate. Problems caused by trisomy 13 or 18 may not be seen with ultrasound.

After birth, your baby may be diagnosed with a physical exam. The doctor may also take a blood sample. This is checked in a lab to find the extra chromosome.

Treatment will depend on your child's symptoms, age, and general health. It will also depend on how severe the condition is. Talk with your child's doctors about the risks, benefits, and possible side effects of all treatments.

Severe, often life-threatening health problems occur in both trisomy 13 and trisomy 18. Treatment for complications varies depending on what body organ is affected and how severe the problem is. Your child's doctor will discuss treatment choices with you.

Researchers don't know how to prevent the chromosome errors that cause these problems. There is no reason to believe that a birth parent can do anything to cause or prevent trisomy 13 or 18 in their child.

If you are younger than 35, the risk of having a baby with trisomy 13 or 18 goes up slightly each year as you get older. After a baby is born with suspected trisomy 13 or 18, a doctor will take a blood sample to do a chromosome analysis. This confirms trisomy 13 or 18. This test also shows the chromosome error that caused the problem. This information is important in assessing the risk in future pregnancies. Translocation and mosaic trisomy 13 and 18 have different risks for future pregnancies.

Your doctor may refer you to a genetic counselor. This expert can explain the results of chromosome tests in detail. They can talk about risks for future pregnancies. The counselor can tell you what tests are used to diagnose chromosome problems before a baby is born.

A diagnosis of trisomy 13 or trisomy 18 can be overwhelming and upsetting. You will face difficult decisions about how to care for your baby. Many babies born with trisomy 13 or trisomy 18 may not live beyond the first few days or weeks of life. So you may have to cope with your baby not coming home from the hospital.

Many resources are available to help you. These include early-intervention services, hospice care, social workers, a hospital chaplain or clergy, and genetic counselors. Support groups for other families dealing with a similar problem can also help you cope with questions and emotions.

If you are caring for your child at home, call your child's doctor if your child has:

• Symptoms that don't get better, get worse, or worry you.
• New symptoms.

• Trisomy 13 and trisomy 18 are genetic problems. They include a combination of birth defects, such as severe learning problems and health problems that affect nearly every organ in the body.
• Most babies born with trisomy 13 or trisomy 18 die by the time they are age 1 year. But some babies with these disorders do survive the first year of life.
• There is no reason to believe that a birth parent can do anything to cause or prevent trisomy 13 or 18 in their child. Researchers don't know how to prevent the chromosome errors that cause these problems.
• A diagnosis of trisomy 13 or 18 can be overwhelming and upsetting. You will face difficult decisions about how to care for your baby.
• Many resources are available to help you. These include early-intervention services, hospice care, social workers, a hospital chaplain or clergy, genetic counselors, and support groups.

Tips to help you get the most from a visit to your child's doctor:

• Know the reason for the visit and what you want to happen.
• Before your visit, write down questions you want answered.
• At the visit, write down the name of a new diagnosis, and any new medicines, treatments, or tests. Also write down any new directions your doctor gives you for your child.
• Know why a new medicine or treatment is prescribed and how it will help your child. Also know what the side effects are.
• Ask if your child's condition can be treated in other ways.
• Know why a test or procedure is recommended and what the results could mean.
• Know what to expect if your child does not take the medicine or have the test or procedure.
• If your child has a follow-up appointment, write down the date, time, and purpose for that visit.
• Know how you can contact your child's doctor after office hours. This is important if your child becomes ill and you have questions or need advice.