Non-Invasive Prenatal Testing (NIPT) is a screening test available during pregnancy. It examines small fragments of fetal DNA that circulate in the pregnant person’s bloodstream. NIPT assesses the likelihood that the fetus may have certain chromosomal conditions.
What NIPT Screens For
NIPT screens for common chromosomal conditions, primarily aneuploidies. These include Down syndrome (Trisomy 21), Edwards syndrome (Trisomy 18), and Patau syndrome (Trisomy 13), which are caused by an extra copy of a specific chromosome. The test can also identify differences in the number of sex chromosomes, such as Turner syndrome (Monosomy X) and Klinefelter syndrome (XXY syndrome). Some NIPT panels also screen for specific microdeletions, where a small piece of a chromosome is missing. NIPT is a screening test, indicating an increased or decreased likelihood of a condition, rather than providing a definitive diagnosis.
When NIPT is Typically Performed
NIPT can be performed as early as 10 weeks of pregnancy and continues to be an option throughout gestation. The timing around 10 weeks is significant because, by this point, there is typically enough fetal cell-free DNA (cfDNA) present in the maternal blood sample for reliable analysis. This cfDNA originates from the placenta and circulates in the mother’s bloodstream. Performing the test too early, before the fetal fraction reaches a sufficient level, may lead to inconclusive results, requiring a repeat test. Early testing allows more time for informed decision-making and any potential follow-up procedures.
Considerations for NIPT Timing
Factors influencing the optimal timing or performance of NIPT include fetal fraction, the proportion of fetal DNA in maternal blood, which can be affected by maternal body weight. Higher body weight sometimes leads to a lower fetal fraction, which might result in an inconclusive test outcome, necessitating a retest. In pregnancies with multiples, NIPT may be less accurate or not recommended. While maternal age is a risk factor for certain chromosomal conditions, its direct impact on fetal fraction is still being investigated. These individual circumstances can guide healthcare providers in recommending the most appropriate time for NIPT or in interpreting results.
Understanding NIPT Results and Follow-Up
NIPT results typically indicate a low-risk (negative), high-risk (positive), or inconclusive outcome. A low-risk result suggests a very low probability of the screened conditions, offering reassurance. A high-risk result, however, does not confirm the presence of a condition but indicates a higher likelihood, necessitating further diagnostic testing for a definitive answer. Common diagnostic procedures include chorionic villus sampling (CVS), which can be performed between 10 and 13 weeks, or amniocentesis, typically done after 15 weeks of pregnancy. Genetic counseling is an important step regardless of the NIPT result, helping individuals understand the implications and available options.