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Introduction ⬇

NT is a noninvasive prenatal screening tool used to alert healthcare providers of potential fetal abnormalities. Ultrasonography is used to assess for a fluid collection at the nape of the fetal neck. An abnormal fluid collection may be due to genetic disorders or fetal physical abnormalities. The test is most accurate at 11–13 weeks’ gestation. This screening test cannot identify fetal abnormalities; it is used as a screening tool for pregnancies that need diagnostic testing. If the NT exceeds the normal range, then diagnostic genetic testing is recommended. There is a relationship between increased fluid in the nuchal area and cardiac abnormalities. The nuchal edema is thought to be a compensation factor in the fetus. It may indicate trisomy 18, trisomy 21 (Down syndrome), or fetal cardiac anomalies.

Procedure ⬆ ⬇

NT screening is performed by specially trained practitioners.

  1. Explain the test purpose and the procedure.

  2. Position the patient on her back as you would for obstetric ultrasound. A coupling gel is applied to the skin of the lower abdomen, and the ultrasound transducer is moved across the abdomen to visualize the fetal neck for fluid accumulation.

  3. NT is determined by ultrasound measurement of fluid in the nape of the neck between 10 and 14 weeks’ gestation.

Clinical Implications ⬆ ⬇

  1. NT screening can alert healthcare providers to potential fetal abnormalities.

  2. A NT measurement of >2.5 mm of fluids in the fetal neck at 11–13 weeks’ gestation is considered abnormal. A NT measurement of ≥3 mm is highly suggestive of fetal abnormalities.

  3. Analyzing maternal serum level of β-hCG and PAPP-A levels, along with NT, increases accuracy of testing for pregnancy that is at risk for fetal abnormalities.

Interventions ⬆ ⬇

Pretest Patient Care

  1. Explain the test purpose and procedure to the patient.

  2. Follow guidelines in Chapter 1 for safe, effective, informed pretest care.

Posttest Patient Care

  1. Review test results; report and record findings. Modify the nursing care plan as needed.

  2. Monitor the patient and counsel appropriately. Educate the patient about further testing (genetic) and genetic counseling.

  3. Follow guidelines in Chapter 1 for safe, effective, informed posttest care.

Interfering Factors ⬆ ⬇

  1. There is a small but significant difference in NT of some ethnic groups (White and Asian fetuses have larger measurements than Black fetuses).

  2. Nuchal cord will decrease accuracy. Color Doppler ultrasound needs to be used in these cases to differentiate cord from fluid.

  3. Improper caliper placement during ultrasound.

Reference Values ⬆

Normal