A new study provides large-scale, population-level evidence that nuchal translucency (NT) screens detect a wide range of genetic disorders at thresholds lower than the level currently considered indicative.
Research published in JAMA Network Open shows fetuses with measurements as low as 2 mm showed an increased risk for chromosomal abnormalities.
In the retrospective cohort study of 414, 268 singleton pregnancies in Ontario, Canada, fetuses with measurements between 3 and 3.5 mm were roughly 20 times more likely to have abnormalities than fetuses with measurements
Fetuses with 2.5-3 mm NT measurements were at a sixfold relative risk (ARR, 5.93; 95% Cl, 5.11-6.88) than the control group, while fetuses within the 2-2.5 range were a little over two times as likely to have an abnormality (ARR, 2.39; 95% Cl, 2.14-2.66).
“Our work reports that the cutoff of 3.5 mm used in our province and in many other jurisdictions may need to be revisited,” said Kara Bellai Dussault, a PhD candidate in epidemiology at the School of Epidemiology and Public Health at the University of Ottawa, Ottawa, Ontario, Canada, and lead author of the study. “Our future work will investigate the best cutoff.”
Ultrasonic NT screenings occur during the first trimester of pregnancy and measure the thickness of a small sac of fluid behind the neck of a gestating fetus. Higher NT measurements indicate that further screening or testing is needed.
The definition of the high-risk threshold varies worldwide but tends to fall between 3 and 3.5 mm. In Denmark and in the United Kingdom, measurements ≤ 3.5 mm are considered normal.
In the United States, the American College of Obstetricians and Gynecologists (ACOG) defines a high-risk NT as 3 mm, or above the 99th percentile for the fetus’s size. But the organization stresses that following guidelines is voluntary and that clinicians should determine whether follow-up testing is warranted on the basis of the condition of the patient, resource availability, and what technology is available.
ACOG also said that clinicians may choose to follow the Society for Maternal-Fetal Medicine or American Institute of Ultrasound in Medicine guidance.
Setting a strict cutoff measurement can be challenging because of the complexity of each case, according to Christina S. Han, MD, Division Director of Maternal-Fetal Medicine and associate clinical professor of obstetrics and gynecology at the University of California, Los Angeles, who was not involved in the study. Clinicians should weigh factors like gestational age, conditions being tested, and whether they consider the 95th or 99th percentile high risk.
The study is important for individual screening programs at hospitals to reconsider their NT testing practices, according to Sulagna C. Saitta, MD, PhD, a geneticist in the Department of Pediatrics and director of reproductive genetics at the David Geffen School of Medicine at UCLA Health, Los Angeles, California, who was not involved in the study.
“I think it’s high time we take a look at” the threshold levels, Saitta said.
Previous research on NT screens has been mostly observational, limited in sample size, and lacking in comparative data for pregnancies that are considered low-risk.
Dussault said she recognized the need for more robust methodological approaches to studying NT. They used data from Canada’s perinatal registry network and included pregnancies with an estimated delivery date over a 5-year period starting in 2016. The average maternal age at delivery was 31.5 years.
Lowering the threshold for the definition of high risk would equate to more women receiving additional screening and testing, such as cell-free DNA (cfDNA), Dussault said. She and her team plan to conduct further studies into the economic implications and risk-benefit analysis of lowering threshold levels.
Dussault said the findings demonstrate the value of NT screenings at an inflection point: Researchers and clinicians are debating if these measurements still add clinical value.
Increasingly, obstetrics programs in the United States favor cfDNA screens because they provide higher accuracy for detecting a limited number of chromosomal abnormalities, including trisomy 21, 18, 13, and sex chromosome aneuploidies, according to Han.
Patients who screen above high-risk thresholds receive further screening, usually a cfDNA or other genetic testing.
NT screenings can indicate a wide range of genetic and nongenetic abnormalities, including heart defects, triploidy, mosaic aneuploidy, and microdeletion syndrome.
“I’ve seen many cases where that NT is the first sign that there’s actually a fetal heart defect, and it has nothing to do with Down syndrome,” Saitta said.
Saitta said an NT result can help expectant parents make better decisions, such as delivering at a higher acuity intensive care unit for newborns.
Otherwise “a mother delivers in some remote area, they can’t handle that baby there so then they ship the baby to [the city],” Saitta said. “The mother remains wherever they are and the baby is now in [the city]. Think about the dynamics of that.”
Bellai Dussault reported support from the Frederick Banting and Charles Best Canada Graduate Scholarships Doctoral Award from the Canadian Institute of Health Research.
Other authors reported receiving a grant from the Ontario Research Fund Genome Canada — CIHR outside the submitted work.
Brittany Vargas is a medicine, mental health, and wellness journalist.
Source link : https://www.medscape.com/viewarticle/new-study-challenges-current-practices-nuchal-translucency-2024a10006mi?src=rss
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Publish date : 2024-04-08 12:10:19
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