NUCHAL TRANSLUCENCY / NASAL BONE - FIRST TRIMESTER
Trimester NT/NB Screen (FTS NT/NB) can reliably assess a mother's risk for having a baby with Down Syndrome, Trisomy 18 and 13 in the first trimester of pregnancy. The ultrasound examination confirms the gestational age of the fetus and measures the nuchal translucency (NT), which is a layer of fluid behind the fetus' neck, and determines the presence or absence of a fetal nasal bone (NB). Maternal blood is sampled using a simple finger stick and then sent to a laboratory for analysis of three biochemical markers: alpha fetoprotein (AFP), free beta human chorionic gonadotropin (free beta hCG) and pregnancy associated plasma protein-A (PAPP-A.) These combined biochemical and biophysical markers yield a detection rate of 96% with a false positive rate of just 2%.
Common Questions
American College of Obstetrics and Gynecology ACOG recommends that all pregnant women, regardless of their age, should be offered screening or diagnostic testing for genetic disorders. There is no one test that is superior to all others and testing should be an informed patient choice, congruent with shared-decision making. Women also have the right to decline both genetic screening and testing, and all decisions should be supported.
Revised Recommendations on Screening and Testing for Genetic Disorders
ACOG Statement March 1, 2016
First Trimester NT/NB Screen is performed when the fetal crown-rump length (CRL) measures between 45 mm and 84 mm, which correlates to 11 weeks, 1 day and 13 weeks, 6 days gestation. If the CRL falls outside these measurements then the test is invalid. For that reason, we recommend that First Trimester NT/NB Screening be scheduled at 12 to 13 weeks gestational age whenever possible.
• Cervical Incompetence
• Uterine Abnormalities
• Ovarian Cysts/Tumors
Fetal gender can be accurately determined accurately after 12 weeks if examined carefully by an experienced sonographer. At 12 weeks both male and female fetuses have a bump protruding between the legs. This represents the developing genitalia. During this stage of development the "bump" begins to angle toward the head (which means boy), or toward the feet, (which means girl.) When a true unobstructed midsagittal (side view) image between the legs can be obtained, the gender can be determined.
While this method of determining gender can be very accurate (85-95%), confirmation of gender will be performed during your 18 to 20 week anomaly scan.
Other Questions
Yes. A detailed fetal assessment performed during the NT scan can detect 30 to 60% of all congenital abnormalities. Additionally, increased NT thickness is also associated with 40% of congenital heart defects.
First Trimester NT/NB scan will include confirmation of gestational age and assessment of the fetus with special attention to the limbs, head, brain, stomach, bladder, spine, abdomen as well as the uterus, placenta, cervix and ovaries.
Head/Brain
Anencephaly, Acrania, Holoproencephaly, Large encephalocele, Cystic Hygroma
Face
Severe Hypotelorism, Severe Micrognathia, Large Clefts, Large Facial Mass
Chest
Abnormal Heart Position, Pleural Fluid
Abdomen
Omphalocele, Gastroschisis, Limb-Body-Wall Complex, Megacystis
Spine
Large Neural Tube Defects, Large Soft Tissue Masses
Extremities
Limb reduction defects, Severe Skeletal Dysplasia
Placenta
Placental Abruption, Previa, Coexisting Molar Pregnancy
What to Expect
The exam will be performed with an external ultrasound transducer. Only on occasion will the use of a transvaginal transducer be necessary. You will remain dressed and asked to lie flat on the exam table with your lower abdomen exposed. Warm gel will be placed on your skin. The sonographer will then position an ultrasound transducer on your abdomen and use varied amounts of pressure to obtain the desired images.
Exam Preparation
Begin drinking 24 oz of WATER before your scheduled appointment time and do not empty your bladder until the procedure has been completed.If your bladder becomes unbearably full prior to your exam, it is ok to partially empty your bladder to relieve pressure.
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