A fetal ultrasound during pregnancy can show features that are suggestive of trisomy 18, and the detection rate is about 90% during pregnancy weeks 14-21. However, an ultrasound may not detect abnormalities until late into the second trimester. Therefore, your doctor may recommend other prenatal screening tests that are more precise.
Noninvasive prenatal screening includes amniocentesis and chorionic villi sampling, which are reasonably accurate methods of diagnosing birth defects:
- Amniocentesis involves removing amniotic fluid from the uterus and examining the cells under a microscope.
- Chorionic villi sampling involves examining the baby’s DNA present in the mother's blood.
After birth, trisomy 18 may be diagnosed by physical examination. Your doctor may order a blood test to look for chromosome abnormality and confirm the diagnosis.
Can trisomy 18 be treated?
About 1 in every 5,000 babies is born with trisomy 18, and most are female. Many babies with trisomy 18 don't survive past the second or third trimester of pregnancy.
Because trisomy 18 causes severe birth defects, almost 50% of babies with the condition do not survive even in the first few weeks of life. Less than 10 out of every 100 babies who survive the initial weeks fail to reach their first birthday. Most babies with the defect who are carried full-term are stillborn.
There is no cure for trisomy 18. Only supportive medical care can be given to provide the baby with the best quality of life possible.
Can trisomy 18 be prevented?
Unfortunately, there is no way to prevent or stop the condition from affecting an unborn child.
The risk of having a baby with trisomy 18 increases with age, most often occurring in women age 35 and older. If your doctor suspects trisomy 18 in the baby, they may perform a chromosome analysis (karyotype) to confirm the diagnosis as well as identify the chromosomal abnormality. Using this information, your doctor can help you determine the likelihood of future pregnancies resulting in trisomy 18.
If you are concerned because of a past pregnancy and feel that your baby may be at risk of the condition, your doctor may refer you to a genetic counselor who can guide you further.
Coping with a diagnosis of trisomy 18
Finding out your baby has trisomy 18 can be overwhelming, and it’s important to get support. Resources that can help parents deal with the emotional distress of having a child with trisomy 18 include:
- Early intervention services
- Hospice care
- Hospital chaplain or clergy
- Social workers
- Genetic counselors
- Support groups
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WebMD. What Is Trisomy 18? https://www.webmd.com/baby/what-is-trisomy-18#1-2
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