Episode Details

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Ultrasound (Abdominal, Transvaginal, and Doppler)

• When they are performed: Transvaginal ultrasounds are especially useful in the first trimester (or in the third trimester to evaluate preterm labor), as they do not require a full bladder. Abdominal ultrasounds are more useful after the first trimester when the uterus is larger.
• What they screen for: Ultrasounds confirm pregnancy, determine gestational age, identify multifetal pregnancies, evaluate fetal growth and position, and check for fetal viability or abnormalities. They also assess maternal structures and amniotic fluid volume. A Doppler ultrasound specifically measures maternal-fetal blood flow. Additionally, an ultrasound assessing nuchal translucency between 11 and 13 weeks of gestation can suggest the presence of Down syndrome (trisomy 21) if increased thickness is found.

Biophysical Profile (BPP)

• When it is performed: Typically used when a nonstress test is nonreactive or if hypoxia is suspected.
• What it screens for: It assesses overall fetal well-being and the risk of chronic fetal asphyxia by combining a nonstress test with an ultrasound to score five variables: fetal heart rate (FHR), fetal breathing movements, gross body movements, fetal tone, and amniotic fluid volume.

Nonstress Test (NST)

• When it is performed: Used widely during the third trimester. For clients with diabetes mellitus, it is performed twice a week starting at 28 to 32 weeks of gestation.
• What it screens for: Assesses for an intact fetal central nervous system (CNS) by monitoring how the fetal heart rate responds to fetal movement. It helps rule out the risk of fetal death.

Contraction Stress Test (CST)

• When it is performed: Indicated for high-risk pregnancies or when a nonstress test result is nonreactive.
• What it screens for: Evaluates how the fetus will tolerate the stress of labor contractions. It checks for uteroplacental insufficiency (which causes late decelerations) and umbilical cord compression (which causes variable decelerations).

Amniocentesis

• When it is performed: May be performed after 14 weeks of gestation. To measure alpha-fetoprotein (AFP), it is ideally done between 16 to 18 weeks. For testing fetal lung maturity, it is done if gestation is less than 37 weeks.
• What it screens for: Early in pregnancy, it assesses for chromosomal disorders or neural tube defects. High AFP levels indicate neural tube defects (like spina bifida), while low levels indicate chromosomal disorders (like Down syndrome). Later in pregnancy, amniotic fluid is tested to determine fetal lung maturity (by measuring the L/S ratio) or fetal hemolytic disease,.

Chorionic Villus Sampling (CVS)

• When it is performed: Ideally performed at 10 to 13 weeks of gestation.
• What it screens for: Acts as a first-trimester alternative to amniocentesis to assess the risk for genetic chromosomal abnormalities.