Increased nuchal translucency (NT) is a measurement taken during an early pregnancy ultrasound. It assesses the small, fluid-filled space at the back of the developing baby’s neck. This measurement screens for the risk of certain conditions. An increased NT measurement is a screening result, not a definitive diagnosis. It indicates a higher likelihood of a condition, prompting further evaluation, but does not confirm a health issue.
Understanding Nuchal Translucency Measurement
Nuchal translucency is measured through an ultrasound, typically performed between 11 weeks and 13 weeks and 6 days of gestation, or when the fetus measures between 45 and 84 millimeters from crown to rump. This timeframe is crucial because the fluid at the back of the neck tends to be reabsorbed after 14 weeks, making accurate measurement difficult. The sonographer obtains a mid-sagittal view of the fetal face and neck to ensure accurate measurement of this translucent area.
An “increased” nuchal translucency measurement signifies that the fluid collection is above a certain threshold for the baby’s gestational age. While a small amount of fluid is normal, a measurement typically above 3 millimeters or the 95th percentile for gestational age suggests an elevated risk. This elevated measurement indicates a higher chance that a chromosomal, structural, or genetic condition might be present, but it does not identify the underlying cause.
Conditions Associated with Increased Nuchal Translucency
Increased nuchal translucency can be associated with various health conditions, though many pregnancies with increased NT measurements result in healthy babies. The presence of excess fluid in the nuchal area is a non-specific marker, meaning it can point to several different types of issues.
Chromosomal conditions are a significant association, with risk increasing proportionally with NT thickness. Common examples include Down syndrome (Trisomy 21), Edwards syndrome (Trisomy 18), and Patau syndrome (Trisomy 13). Increased NT can also be associated with Turner syndrome, a chromosomal condition affecting females.
Beyond chromosomal anomalies, structural heart defects are frequently linked to increased NT. Fetuses with increased NT have a higher likelihood of congenital heart defects, with risk increasing with NT value. Other structural anomalies, such as diaphragmatic hernias, exomphalos (abdominal wall defects), or skeletal abnormalities, can also be associated with an enlarged NT.
In some cases, increased NT may indicate specific genetic syndromes. Noonan syndrome is one genetic condition clearly associated with increased nuchal translucency, even with a normal karyotype. Microdeletion syndromes, involving tiny missing genetic material, can also be a factor.
Diagnostic Steps Following an Increased Measurement
Following an increased nuchal translucency measurement, healthcare providers typically offer further investigations. These steps help assess the baby’s health comprehensively and provide definitive information. The decision to pursue these tests is personal, made in consultation with medical professionals.
One common next step is Non-Invasive Prenatal Testing (NIPT). This blood test analyzes fragments of fetal DNA circulating in the mother’s bloodstream to screen for common chromosomal conditions like Down syndrome, Trisomy 18, and Trisomy 13 with high accuracy. While highly sensitive, NIPT remains a screening test and does not provide a definitive diagnosis.
A detailed ultrasound, often referred to as a fetal anatomy scan or fetal echocardiogram, is usually recommended later in pregnancy, typically around 18 to 22 weeks. This specialized ultrasound examines the baby’s organs and structures in detail, paying particular attention to the heart given the strong association between increased NT and cardiac defects. This scan can identify or rule out many structural anomalies.
For a definitive diagnosis, invasive diagnostic tests such as Chorionic Villus Sampling (CVS) or Amniocentesis may be offered. CVS is performed earlier in pregnancy (10-13 weeks) and involves taking a small sample of placental tissue for genetic analysis. Amniocentesis is typically done after 15 weeks, collecting a small amount of amniotic fluid. Both procedures provide a definitive chromosomal diagnosis, but they carry a small risk of complications, including miscarriage.
What an Increased Measurement Can Mean
An increased nuchal translucency measurement can lead to various outcomes. In many cases, even with an initial increased measurement, the baby is born healthy with no identifiable issues after all follow-up tests are normal. This highlights that an increased NT indicates a risk, not a certainty.
If subsequent diagnostic tests, such as CVS or amniocentesis, identify a specific condition (e.g., chromosomal anomaly, structural defect, or genetic syndrome), this information allows parents to prepare and make informed decisions about their pregnancy and the care their child may need. Early diagnosis can facilitate access to specialized medical care and support resources.
In some instances, the NT measurement is increased, but all follow-up tests (including chromosomal analyses and detailed ultrasounds) come back normal. This is called an “isolated” increased NT. While the risk of certain conditions remains slightly elevated compared to the general population, studies show that the vast majority of these babies are healthy. For instance, even with NT measurements equal to or greater than 5.5mm, approximately 80% of fetuses with normal karyotypes had a normal outcome in one study.
Genetic counseling plays a key role throughout this process. Genetic counselors provide information about test results, explain implications of increased NT, discuss further testing options, and offer emotional support. This guidance helps parents navigate complex medical information and make decisions aligned with their values and circumstances.