Non-invasive prenatal testing (NIPT), also known as cell-free DNA (cfDNA) screening, is a widely used method for expectant parents to gain early insights into their baby’s genetic health and identify the risk of certain chromosomal conditions. Beyond screening for genetic disorders, NIPT offers the possibility of determining the baby’s sex, often earlier than traditional ultrasound methods. However, a common question arises: can these highly accurate gender blood tests sometimes be incorrect?
How Gender Blood Tests Work
NIPT analyzes small fragments of cell-free fetal DNA (cffDNA) released by the placenta into the pregnant person’s bloodstream. A blood sample is taken and sent for analysis.
The core principle behind gender determination through NIPT involves identifying sex chromosomes. If the test detects the presence of a Y chromosome, it indicates a male fetus, as biological males typically have XY chromosomes. Conversely, if no Y chromosome is found and only X chromosomes are identified, the fetus is indicated to be female. While NIPT is highly accurate, typically reporting 98% to 99.9% accuracy for gender determination, its reliability generally increases after 10 weeks of gestation as more cffDNA becomes available.
Reasons for Inaccurate Results
Despite NIPT’s high accuracy for gender prediction, various factors can occasionally lead to an incorrect result. It is important to remember that NIPT is a screening test, not a diagnostic one, meaning it indicates risk rather than providing a definitive diagnosis.
One common reason for inaccurate or inconclusive results is insufficient fetal DNA in the maternal bloodstream, often referred to as low fetal fraction. If the blood sample is taken too early in the pregnancy, usually before 10 weeks, there may not be enough cffDNA for an accurate analysis, potentially leading to a false female result. Maternal factors like higher body mass index (BMI) can also result in a lower concentration of fetal DNA, impacting the test’s ability to accurately detect the Y chromosome.
The phenomenon known as vanishing twin syndrome can also influence NIPT gender results. If a twin pregnancy was initially conceived but one fetus was lost early in development, its DNA, including a Y chromosome if it was male, can still circulate in the mother’s blood for a period. This residual male DNA can lead to a false male result for the surviving female twin.
Certain maternal biological conditions can also introduce male DNA into the mother’s system, causing a false male result. Examples include a prior organ transplant from a male donor or a recent blood transfusion involving male blood. These external sources of Y chromosomes can be mistakenly attributed to the fetus by the NIPT, leading to an incorrect gender prediction.
Rare fetal chromosomal abnormalities might also affect the NIPT’s gender determination. Conditions involving variations in sex chromosomes, such as Turner syndrome (XO) or Klinefelter syndrome (XXY), can sometimes present atypical Y chromosome signals. While NIPT can screen for these conditions, they can also lead to unexpected gender results. Additionally, although rare, human error or sample contamination during the collection or laboratory processing can occur, contributing to an inaccurate result.
What to Do About Unexpected Results
The initial and most advisable step is to discuss NIPT results thoroughly with a healthcare provider, such as an obstetrician or genetic counselor. They can explain the specific findings, consider any contributing factors, and guide parents on the next appropriate actions.
Healthcare providers often recommend confirmatory tests if there is a discrepancy or concern about the NIPT gender result. A detailed ultrasound, typically performed around 18 to 22 weeks of pregnancy, is a common and non-invasive method to visually confirm the fetal sex. Ultrasounds are generally accurate for gender determination, though factors like fetal position can sometimes affect visibility.
In situations where there are medical reasons beyond gender determination, such as concerns about chromosomal abnormalities, more invasive diagnostic tests might be suggested. These include amniocentesis or chorionic villus sampling (CVS), which involve collecting fetal cells directly for genetic analysis. These diagnostic procedures offer near 100% accuracy for sex determination but carry a small risk of complications, so they are not typically performed solely for gender confirmation.