When do you test for trisomy 18

Close Alert Banner. What is Prenatal Screening? What Do We Screen For? Trisomy 18 Decrease text size Default text size Increase text size. Print This Page.

Facebook LinkedIn Twitter Email. Trisomy Trisomy refers to a person having three copies of a chromosome, instead of the typical two. Trisomy 18 also called Edwards syndrome , is a condition that is caused by an extra copy of chromosome This generally occurs in the sperm or the egg that conceived the baby. The extra copy of chromosome 18 is usually found in every cell of a person's body.

Trisomy 18 is also called "Edwards syndrome" and trisomy 13 is also called "Patau syndrome" after the physicians who first described the disorders. What causes trisomy 18 and trisomy 13? When this cell contributes the extra chromosome 18 to the embryo, trisomy 18 results. When this cell contributes the extra chromosome 13 to the embryo, trisomy 13 results. What types of problems do children with trisomy 18 and trisomy 13 typically have?

Trisomy 18 thin and frail babies with a weak cry feeding problems small head size with the back of the head prominent ears are usually low-set on the head mouth and jaw unusually small shortened sternum breastbone about 90 percent of babies have heart defects clenched fists difficulty extending fingers contracted joints spina bifida , eye problems, cleft lip and palate , and hearing loss may be present seizures high blood pressure and kidney problems scoliosis curvature of the spine in males, the testes fail to descend into the scrotum.

Trisomy 13 low birthweight small head with a sloping forehead usually there are major structural problems with the brain including holoprosencephaly, when the brain does not divide properly close-set eyes underdeveloped nostrils eye problems ears low-set and unusually shaped scalp abnormalities that resemble ulcers birthmarks that are purplish-red extra fingers and toes polydactyly feet with prominent heels heart defects , kidney problems omphalocele , a condition in which some of the abdominal organs protrude through an opening in the abdominal muscle around the umbilical cord in males, testes may fail to descend into the scrotum females may have abnormally shaped uterus, or a bicornuate uterus.

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Kevin B. Churchwell, President and CEO. Connect with Boston Children's Hospital. The reflected sound waves will be digitally converted into images on a monitor. Your health care provider or the technician will use these images to measure the size of the clear space in the tissue at the back of your baby's neck.

Your health care provider will use your age and the results of the blood test and ultrasound exam to gauge your risk of carrying a baby with Down syndrome or trisomy Other factors — such as a prior Down syndrome pregnancy — also might affect your risk. First trimester screening results are given as positive or negative and also as a probability, such as a 1 in risk of carrying a baby with Down syndrome.

First trimester screening correctly identifies about 85 percent of women who are carrying a baby with Down syndrome. About 5 percent of women have a false-positive result, meaning that the test result is positive but the baby doesn't actually have Down syndrome. When you consider your test results, remember that first trimester screening indicates only your overall risk of carrying a baby with Down syndrome or trisomy A low-risk result doesn't guarantee that your baby won't have one of these conditions.

Likewise, a high-risk result doesn't guarantee that your baby will be born with one of these conditions. If you have a positive test result, your health care provider and a genetics professional will discuss your options, including additional testing. For example:. Your health care provider or a genetic counselor will help you understand your test results and what the results mean for your pregnancy. Mayo Clinic does not endorse companies or products.

Advertising revenue supports our not-for-profit mission. This content does not have an English version. This content does not have an Arabic version. Overview Nuchal translucency measurement Open pop-up dialog box Close. This is called a false-negative test result. A false-positive result can cause stress and lead to unnecessary testing such as chorionic villus sampling [CVS].

Many women who have a positive screening test result are actually carrying a healthy baby. A "positive" result means that there is a higher-than-average chance your baby has Down syndrome or trisomy If the result is "negative," it means that your baby probably doesn't have those birth defects. But it doesn't guarantee that you will have a normal pregnancy or baby. Your doctor may tell you the result of your test as a set of numbers.

Doctors often use a certain number as a cutoff for a positive result. For example, your doctor may say the cutoff is 1 out of This means that if your result is 1 out of or 1 out of a number less than such as 1 out of , you have a positive result and your baby has a higher chance of a birth defect. If your result is 1 out of , this means that you have a negative result and your baby has a lower chance of a birth defect. If you have a positive test result, your doctor may want you to have the diagnostic test chorionic villus sampling CVS or an amniocentesis test in the second trimester to find out if your baby has a problem.

But it's your choice whether to have another test. If you have a negative result, you may choose not to have any more tests. Deciding whether to have a test for birth defects is a personal decision. And it can be a hard choice. You need to think about what the results of a test would mean to you and how they might affect your choices about your pregnancy. If you choose to have a test, you may want to talk with a genetic counsellor.

The counsellor can talk with you about the reasons to have or not have the test. He or she can also help you find other resources for support and decision-making. Author: Healthwise Staff. This information does not replace the advice of a doctor.