Genetic Disorders and Pregnancy: What Parents-to-be Should Know

9 August 2018, Prof. Dr. Vidhaya Mekanandha, Pediatric Geneticist, Children’s Center, Bumrungrad International Hospital

The sequencing of the human genome 15 years ago represented a major scientific milestone. That breakthrough has led to a number of medical improvements, including the ability to detect genetic and chromosome disorders during pregnancy with highly accurate, non-invasive genetic tests.

For expectant mothers and fathers-to-be, here is what you should know about genetic and chromosome disorders.

Chromosome disorders are rare occurrences

It is important not to overstate the risk that a baby will be born with a genetic or chromosome disorder. The most common chromosome disorder, Down syndrome, also known as trisomy 21, occurs once in every 1,000 to 1,100 births. Edwards syndrome (trisomy 18) is present in one out of 6,000 births. Patau syndrome (trisomy 13) occurs once in every 6,500 births.

Risk factors include age and inherited risks

The age of the expectant mother is a significant risk factor for genetic or chromosome disorders. Risks increase along with the age of the pregnant woman, with significantly higher risks among those age 35 and older.

Other risk factors include: parents having another child with a genetic disorder; one parent having a chromosome disorder; and a family history of genetic disorders. Chromosomal abnormalities in a baby may be inherited from one or both parents, but they can also occur with no family history.

Some risks are controllable

In addition to age and inherited factors, environmental and medical factors — exposure to radiation or hazardous chemicals; rubella, herpes simplex and certain other viral infections; alcohol consumption; eating tainted or toxic foods, among others — may result in genetic mutations or variants either before or during pregnancy. Avoiding or reducing these controllable factors can lower an individual’s risk for passing a disorder onto the fetus.

Prenatal testing is non-invasive and highly accurate

Genetic screening tests during pregnancy have greatly improved in recent years. The most reliable prenatal test now in wide use is known as NIFTY (or Non-Invasive Fetal TrisomY test). NIFTY uses advanced genetic sequencing technology to analyze the fetal DNA present in the mother’s blood sample.

  • The test is highly reliable — accurate to over 99%, with below 1% false positive rate — and screens for the three most common trisomy conditions: Down syndrome, Edwards syndrome (trisomy 18), and Patau syndrome (trisomy 13), as well as other genetic disorders caused by missing or extra genetic information in the DNA of the fetus.
  • NIFTY offers a significant advantage in accuracy compared to conventional prenatal screening tests, including ultrasound scans and maternal serum testing. And because NIFTY is a non-invasive test — unlike amniocentesis or other invasive procedures — there is zero added risk of miscarriage and no other side effects for the mother or the fetus.
  • The NIFTY test can be administered as early as the tenth week of pregnancy. The test involves a simple blood draw from the pregnant woman, and test results are available in two to three weeks.

Earlier awareness expands options

Prenatal genetic testing is generally used in situations where risk factors are present, such as age or family history; it is not recommended for all pregnancies. Those who prefer having the test usually mention one or both of the following as being important factors for their decision:

  • Considering the very high likelihood of favorable results, testing provided a feeling of reassurance and a sense of relief that there was now one less thing to worry about for the remainder of the pregnancy.
  • Having a test early in the pregnancy that showed the presence of a chromosome disorder at the very least allowed for more time to understand the specifics of the particular disorder and prognosis, and meant additional options could be considered before deciding about continuing with the pregnancy. This was particularly valued in situations involving trisomy 13 and trisomy 18, where survival beyond one year is unlikely.

Editor’s Note: This article has been reprinted here with permission of Bumrungrad International Hospital.

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