Becoming pregnant at an advanced maternal age (35 and older) carries an increased risk of trisomy disorders in children. A common trisomy chromosomal disorder that develops in babies born to mothers of advanced maternal age is Edwards’ syndrome, a chromosomal abnormality characterized by 3 copies of chromosome 18. For this reason, Edwards’ syndrome is also known as trisomy 18.
How Common is Edwards’ Syndrome?
Edwards’ syndrome occurs in roughly 1 in 6,000 live births,. Of those live births, approximately only half live longer than one week and only about 5-10% of children live beyond their first birthday.
How Does Edwards’ Syndrome Occur?
A healthy individual carries 2 copies of each chromosome, whereas individuals diagnosed with Edwards’ syndrome have a karyotype (set of chromosomes) with 3 chromosome 18s. This phenomenon occurs when there is an abnormality in the behavior of the egg and sperm at the time the fetus is conceived.
Trisomy 18 occurs in two events known as nondisjunction and mosaicism. Nondisjunction accounts for more than 90% of cases of Trisomy 18 and results in every cell containing three chromosome 18s. In cases where mosaicism is the cause, only part of an individual’s cells contain an extra copy of chromosome 18.
Partial Trisomy 18 is an inheritable chromosome abnormality that is passed onto a child from an individual who has a translocation or rearrangement of chromosome 18 with another chromosome. The individual with the translocation is considered a carrier of the condition, but does not exhibit signs of Edwards’ syndrome themselves.
Edwards’ Syndrome Characteristics
Infants with Edwards’ syndrome typically display the following physical features:
- Clenched hands
- Overlapping fingers
- “Rocker bottom feet”
- Ears that are set lower than usual
- Small head
- Cleft lip or palate
- Exomphalos (a sac outside of the abdomen)
Diagnosing Edwards’ Syndrome
Prenatal screening may be performed to detect the probability of your baby having a chromosomal condition. Through the use of ultrasound and a variety of blood tests, screening may give insight into the risk associated with each pregnancy.
New non-invasive fetal trisomy tests offers technologically advanced screening without the risks of invasive procedures. Non-invasive screening can be performed as early as week 10 of gestation and requires a simple blood draw from the mother.
If screening tests results show high risk, your physician may recommend further, diagnostic testing options.
Diagnostic testing is used to obtain a definitive answer after a screening test shows the fetus has a high probability of having a chromosomal abnormality or birth defect. These tests are generally invasive. The most common invasive prenatal diagnostic tests offered are Chorionic villus sampling (CVS) and amniocentesis, which test for conditions such as trisomy 21, 18, and 13, as well as neural tube defects. CVS is performed between weeks 10 to 12 of pregnancy and amniocentesis is performed between weeks 15 and 18.
Speak With Your Physician or Genetic Counselor About Testing Options
If you are of advanced maternal age, have a family history of genetic disease, or have had a previous pregnancy with a chromosomal abnormality, speak with your healthcare provider or a genetic counselor about screening or diagnostic testing. These trained professionals will help you understand each test, how each is performed, and how to interpret the results.
With early detection, Edwards’ syndrome may be diagnosed before birth. Having this information early allows parents time to prepare for any necessary treatments the child may need at the time of birth.