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Advances in prenatal genetic screening continue to expand the options available to expectant parents. During a recent episode of BackTable Women’s Health, Dr. Nicole Faulkner spoke with Dr. Andrei Rebarber about single-gene noninvasive prenatal testing (sgNIPT), carrier screening, and how these tools can help guide pregnancy management. Their discussion explored how prenatal screening has evolved, when different tests may be appropriate, and why understanding test results is just as important as the testing itself.

The Evolution of Prenatal Genetic Screening

Prenatal genetic screening has changed dramatically over the past several decades. In the 1980s and 1990s, ultrasound was commonly used to identify fetuses with certain genetic conditions, particularly Down syndrome. While helpful, ultrasound screening produced a relatively high number of false positives and had limited detection rates.

During that time, maternal age played a significant role in determining who qualified for diagnostic testing. Patients aged 35 and older were often offered amniocentesis, while younger patients generally did not receive further evaluation.

By the late 1990s and early 2000s, first-trimester nuchal translucency screening became more common. Measuring the thickness at the back of the fetal neck provided another marker for chromosomal abnormalities and helped improve risk assessment.

A major advancement came around 2010 with the introduction of cell-free DNA testing. This screening analyzes fragments of placental DNA that naturally circulate in the mother’s bloodstream throughout pregnancy. Because the placenta continually renews itself during gestation, these DNA fragments provide valuable genetic information through a simple maternal blood draw.

Understanding Carrier Screening

Carrier screening helps determine whether prospective parents carry genetic variants associated with inherited conditions. For autosomal recessive disorders, both parents must be carriers for there to be a risk of having an affected child. Even when both parents are carriers, there is only a one-in-four chance that a pregnancy will be affected.

Dr. Rebarber explained that modern carrier screening panels have expanded significantly. Current panels can screen for up to approximately 770 recessive conditions. Larger panels have become increasingly practical because they are more cost-effective to run than multiple smaller tests.

Conditions included in these panels are selected based on several factors, including how frequently they occur within the population and how severe they are. Some conditions can cause cognitive or intellectual disabilities, while others benefit from early intervention immediately after birth. Certain disorders may even cause complications during pregnancy that require specialized monitoring from maternal-fetal medicine specialists.

Because of the diverse population in the United States, larger pan-ethnic screening panels often provide greater clinical value than ethnicity-specific testing. Although many individuals will be identified as carriers for at least one condition, the likelihood that both partners carry the same recessive condition is relatively low, approximately one to two percent.

What Is Single-Gene NIPT?

Single-gene noninvasive prenatal testing (sgNIPT) builds on cell-free DNA technology by screening for specific inherited single-gene disorders using placental DNA circulating in the mother’s blood.

Currently available tests evaluate panels that include either 14 or 21 autosomal recessive conditions. Separate panels are also available for approximately 30 autosomal dominant disorders.

Unlike carrier screening, which identifies whether parents carry certain genetic variants, sgNIPT evaluates the pregnancy itself to estimate the likelihood that the fetus has one of the screened conditions.

Testing can be performed at any time after 10 weeks of pregnancy.

When Can sgNIPT Be Helpful?

According to Dr. Rebarber, the usefulness of sgNIPT depends on the individual patient.

One common challenge occurs when maternal carrier screening identifies a genetic variant, but partner testing cannot be completed because the father is unavailable or unable to undergo testing. In these situations, sgNIPT may provide additional information without requiring an invasive diagnostic procedure.

Many patients also prefer to avoid invasive testing whenever possible. While sgNIPT is not considered diagnostic, it can help identify pregnancies that may benefit from closer monitoring, additional counseling, or delivery planning.

Early knowledge allows healthcare providers to coordinate care with neonatologists and pediatric specialists, determine the most appropriate delivery location, and begin planning treatment as early as possible. In some conditions, maternal treatment during pregnancy may even improve fetal outcomes.

Screening Versus Diagnostic Testing

Although screening technology continues to improve, diagnostic procedures remain the standard of care when definitive answers are needed.

If both parents are known carriers for the same recessive condition, diagnostic testing through chorionic villus sampling (CVS) or amniocentesis is recommended because these procedures directly analyze fetal genetic material.

CVS is typically performed between 11 and 13 weeks of pregnancy and can be completed through either an abdominal or vaginal approach.

Amniocentesis is generally performed between 16 and 18 weeks using a needle inserted into the amniotic sac.

Dr. Rebarber noted that miscarriage rates associated with these procedures have decreased significantly over time, making them safer than in previous decades.

Interpreting Genetic Test Results

Understanding what a positive result actually means is an essential part of prenatal genetic counseling.

A positive screening result indicates an increased risk, not a confirmed diagnosis. Medical literacy plays an important role in helping patients understand this distinction.

For pregnancies with positive findings, referral to a genetic counselor or medical geneticist allows families to better understand the specific condition and what the results may mean. For example, cystic fibrosis exists on a spectrum depending on the particular genetic mutation identified.

Carrier screening is ideally completed before pregnancy whenever possible. For patients pursuing IVF, identifying carrier status before embryo transfer may allow selection of unaffected embryos.

Evaluating New Research

As prenatal screening technology continues to evolve, Dr. Rebarber emphasized the importance of carefully evaluating new research.

Study design matters. Retrospective studies may contain more bias and confounding factors than prospective studies. Many retrospective studies only confirm positive screening results without verifying negative results, making it difficult to fully assess test performance.

Some genetic conditions also do not become clinically apparent until later in life, creating additional challenges when measuring accuracy.

Because of these limitations, positive predictive value, the likelihood that a positive result truly represents an affected pregnancy, remains one of the most important measures when interpreting the clinical usefulness of any screening test.

Why Early Prenatal Genetic Screening Matters

Single-gene NIPT represents another advancement in prenatal genetic screening, offering additional information for select inherited conditions through a simple blood test after 10 weeks of pregnancy. While it does not replace diagnostic procedures such as CVS or amniocentesis, it can provide valuable information when partner testing is unavailable or when patients wish to avoid invasive testing.

Combined with appropriate carrier screening, genetic counseling, and individualized clinical care, these evolving technologies continue to improve pregnancy management and help families make informed decisions throughout pregnancy.

Contact Us

If you have questions about prenatal genetic screening or want to learn which testing options may be right for your pregnancy, contact the maternal-fetal medicine specialists at Maternal Fetal Medicine Associates through the online contact form. Our team is here to provide expert guidance, personalized recommendations, and compassionate care every step of the way.

Carnegie Imaging for Women blogs are intended for educational purposes only and do not replace certified professional care. Medical conditions vary and change frequently. Please ask your doctor any questions you may have regarding your condition to receive a proper diagnosis or risk analysis. Thank you!