Prenatal genetic screening and what parents-to-be need to know

[Parenting NH Administrator]

By Erica S. Stelmach, MS CGC

 

During pregnancy, parents-to-be will be asked if they want genetic screening for their baby. This is a standard question, but it can also be an overwhelming one. You may wonder what genetic screening is all about and if it is something you should do.

 

Genetic screening in pregnancy is intended to screen for three conditions: Down syndrome, trisomy 18 and spina bifida. Normally these conditions are not inherited; they usually result from random events that happen just before or just after conception.

 

Down syndrome usually causes mild to moderate mental impairment, certain types of birth defects, changes to facial features and short stature. Trisomy 18 is a lethal condition and causes birth defects, profound mental impairment and neurologic damage. Spina bifida is a birth defect that leads to nerve damage and permanent physical disability of varying degrees.

 

The standard kind of genetic screening is done using a combination of ultrasound and blood work. An ultrasound is done at 11 to 14 weeks to date the pregnancy and measure the size of the fluid pocket at the back of the baby’s neck called the nuchal translucency measurement. Blood work is combined with the ultrasound result to calculate a risk number for each condition. The result that you get from this type of screening tells you the chance that your baby will have each condition. This type of screening can never say for certain whether the baby has one of these conditions.

 

There are several different ways genetic screening can be done, and they vary in their accuracy, speed of results and number of blood draws. You should discuss your options with your obstetrician or midwife to help determine which method of screening works best for you. In some cases you may be referred to a prenatal genetic counselor to discuss these options in more detail. A prenatal genetic counselor is a healthcare professional with specialized training in genetic disorders and genetic screening in pregnancy.

 

Genetic screening results fall into one of two categories: negative or positive. A negative result means the risk number is low and the baby is unlikely to have the condition. A positive result means that the risk number is high enough to warrant consideration of further testing. (Genetic screening is not designed to say for certain if there is a problem in the baby so some people will get a false positive or a false negative result.) Couples who receive a positive result may be referred to a genetic counselor to discuss the finding and the options for additional screening and testing.

 

You may have heard about a new kind of blood test for genetic screening, one that is more accurate than the standard screening methods. This type of screening is called non-invasive prenatal testing. Because of the greater accuracy this type of screening can be an attractive option. However, this screening is still very new and careful consideration of all of the potential benefits and limitations is important. I recommend expectant parents considering non-invasive prenatal testing speak with a genetic counselor to discuss this option in detail.

 

Genetic screening poses no risk to the baby and can alert expectant parents to potential concerns, but it is not required. For some expectant parents, genetic screening is a helpful tool, while others find it confusing, and even a little scary. It is important to discuss genetic screening with your obstetrician, midwife, and/or genetic counselor so you can decide if it is right for you.

Erica S. Stelmach, CGC, MS, is a genetic counselor at Dartmouth-Hitchcock Specialty Care at Bedford Medical Park. For more information, go to Dartmouth-Hitchcock.org.