Fetal DNA Testing – New Parameters

Noninvasive prenatal testing (NIPT) of DNA is a new and expanding option for pregnant women.
Research has shown it to be accurate for detecting trisomy, in women who are considered low or high risk. Trisomy exists when there are three copies of a chromosome instead of the normal two. Clinical studies have pointed to the accuracy and safety of individual non-invasive tests. These have been found to detect suspect trisomies such as Down Syndrome nearly 100% of the time.
New guidelines are emerging regarding NIPT, despite the cautious optimism of medical societies. A Royal College of Obstetricians & Gynecologists study favors it. The organization, however, issued a statement regarding the method’s sensitivity and possible reasons test errors may occur in the processing, not the science. Factors can include gestational age, maternal obesity, placental abnormalities, and twins.
A paper by the Society of Maternal Fetal Medicine identifies NIPT as promising, yet current practices and recommendations should remain in place. The organization emphasizes a need for evaluating the test method for additional types of trisomies, specifically with cell-free fetal DNA.
Nonetheless, noninvasive testing seems to be catching on. Expanded use and additional studies promise to make this method more widespread. Findings on its accuracy and benefits are catching the attention of the general population and the medical community.
Accuracy Rates
Non-invasive prenatal testing is a viable method for detecting several leading chromosomal abnormalities. For example, it exhibits a 99%+ detection rate for trisomy 21, or Down Syndrome, according to the NCHPEG and a BlueCross BlueShield technology assessment mentioned in an Oxford Health Plans, LLC clinical report.
Additional findings include:
• Trisomy 18 (Edward’s Syndrome): Similar to that of trisomy 21, the detection rate has been found to be 98-99%.
• Trisomy 13 (Patau Syndrome): The NHCPEG cites a 79-92% detection rate. If a pregnancy involves an affected fetus, the condition might not be detected, so traditional testing is needed to confirm a diagnosis if Patau is suspected.
False positive rates of about 1% have also been found. Even if a positive result is indicated, additional testing is often recommended following NIPT. False negative results happen, as well, which is why many laboratories provide a risk score with reports. In some cases, insufficient levels of fetal DNA in a sample can skew the test results. Aside from these possibilities, non-invasive testing is highly effective in detecting the most common trisomies.
How It Works
Non-invasive fetal DNA testing is performed using the mother’s blood. There are a couple of methods.
Massive parallel shotgun sequencing is used to measure the proportion of targeted chromosomes and compare the number with standard guidelines.
Another way is to compare specific parts of the chromosome with what is expected. Laboratories can report the results as positive or negative, consistent with specific conditions, or as a percentage of risk. For those with insurance, coverage can vary depending on the policy because the test is new.
Benefits
NIPT is a low-risk test method that can be performed relatively early in pregnancy. Results can be obtained in a week, though sometimes longer. Methods such as amniocentesis and chorionic villus sampling (CVS), on the other hand, can take up to two weeks. An ultrasound is not needed for interpreting results or guiding physicians during the procedure.
• Risk: The new testing can detect and analyze fetal cell-free DNA fragments without penetrating the womb. These are found in the mother’s blood from 8 weeks on. NIPT requires just a blood test, without the risks of traditional, more invasive procedures such as CVS or amniocentesis. In rare cases, these more invasive methods can harm the baby or trigger miscarriage.
• Recommendations: For pregnant women 35 or older, NIPT is a safer procedure. Testing is also suggested if ultrasound results point to an increased risk, or if someone previously was pregnant and there was a chromosomal condition involved. Positive test results in the early trimesters should be followed up with NIPT later on. Use guidelines also suggest false positives be confirmed using CVS or amniocentesis.
Long-Term
Major medical societies anticipate NIPT will expand in the long term. For some chromosomal abnormalities, it is almost as accurate as other diagnostic methods. Its accuracy has primarily been proven in higher risk cases. Usefulness in low risk pregnancies is expected to be gauged soon according to an NHCPEG factsheet. Future studies may also weigh in on NIPT for pregnancies involving more than two fetuses or egg donations. More women are electing to have the non-invasive test. More data will therefore provide updated results on performance and accuracy concerning a range of factors and conditions.