Screening for birth defects: What parents need to know

Last Modified: 3/04/2021

birth defects

Prenatal tests and screenings can help reveal information about your health as well as your unborn child’s. They can be instrumental in detecting birth defects and genetic diseases, aiding in healthcare decisions you might need to make before and after your child’s birth. With that said, it’s important for parents to understand their options, which is why we’ve asked Danielle Berdahl, MD, PPG – Maternal-Fetal Medicine, to expand further on the subject.

What are birth defects?

Birth defects are any structural change or abnormality present at birth that can affect the body.

Are there different types of birth defects?

Yes, birth defects that have medical, surgical or significant cosmetic consequences are considered major malformations. The occurrence of major malformations is low, ranging anywhere from 2-4%. Minor abnormalities, on the other hand, are far more common.

What causes birth defects to occur?

Birth defects can occur in any stage of pregnancy and are due to abnormalities in internal fetal growth or external factors that interfere with development or modify a previously normal structure. Factors that could potentially contribute to an increased risk for malformations include:

  • Genetics
  • Low folate levels
  • Alcohol use
  • Illegal drug use
  • High lead levels
  • Extremes of heat or fevers
  • Certain infections
  • Certain medications and chemicals
  • Environmental factors
Who is at risk for birth defects?

The overall risk of most major birth defects does not vary significantly across ethnic groups. The type of malformation is more inconsistent and may be related to an increased genetic risk and environmental factors. Additionally, women age 35 and older, plus those with severe morbid obesity or other health risks, including factors mentioned above, will have a higher baseline rate than the general population.

Can birth defects be prevented?

While not all birth defects can be prevented, there are some steps women can take to decrease their risk. One step includes incorporating a prenatal vitamin with folic acid several months before attempting to conceive. This step has been shown to reduce the risk for neural tube (spinal) and some cardiac defects. Additionally, parents-to-be should set up a pre-conceptual visit to review chronic health problems, medications, immunization status for certain infections, family history and pre-pregnancy planning.

How are birth defects diagnosed, and at what stage?

Diagnosis can vary depending on the cause, severity, presentation and timing of the birth defect. Some major defects can be recognized as early as the end of the first trimester. Women at high risk for abnormalities based on history or abnormal testing may be offered an earlier anatomy scan at 16 weeks of pregnancy. For most women at average risk, a screening ultrasound at 20 weeks is sufficient. Those women at an increased risk, or those with concern at an anatomy ultrasound, should have a more specialized ultrasound with maternal-fetal medicine specialists (MFM). It is important to note that some abnormalities may not be detectable until late in the pregnancy or until after the infant is born. Still, not all abnormalities can be detected by ultrasound.

What types of screenings are available to parents?

Birth defect screenings can take various forms. Screening for common trisomies can occur in the first trimester with a first-trimester screen, blood test and specialized ultrasound, or cell-free DNA testing. The Quad screen is another form of genetic screening that can be completed in the second trimester. All pregnant women should get an anatomical screening ultrasound at 20 weeks to assess for structural abnormalities.

How accurate are the current screenings?

All genetic screening tests can have a false positive and false-negative rate. This rate can vary between the test and individual disorder up for assessment. Positive screening results require further evaluation for confirmation. Ultrasound detection of abnormalities is affected by the location and level of ultrasound performed and factors such as maternal body type, fetal positioning and gestational age at the time of the scan.

What are the benefits and risks associated with these screenings?

Families must discuss their goals from screening and the limitations of the test with their provider. Early diagnosis of a genetic abnormality can allow the family time to gather knowledge and prepare for the child’s condition. It can also allow for extra observation to help decrease the risk for stillbirth if elevated.

Additionally, intrauterine fetal surgery is also a possibility for certain conditions. Some structural abnormalities could require immediate specialized care for the infant, affecting the location for delivery. With that said, not all positive screens are associated with an actual abnormality. Some families will undergo the stress of the possible diagnosis and cost of evaluation for a normal outcome.

If there is confirmation of a birth defect, what are the parents’ next steps?

If a birth defect is suspected or confirmed, consultation and specialized ultrasound with maternal-fetal medicine should be performed. Genetic testing may also be offered. Any additional information obtained will help provide education on the abnormality and development of a plan for the pregnancy and delivery. This might include other specialists required for fetal and/or neonatal care to achieve the best outcome for both mother and child.

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