OB: EARLY PREGNANCY PRENATAL TESTING Flashcards
Chromosome 21
Down
Chronosome 18
Edwards
Chromosome 13
Patau
When does a womens risk of aneuploidy in pregnancy increase?
A woman’s age (risk of aneuploidy increases substantially with age, especially over 35) and the screening results determine her risk.
When is first trimester screening often performed?
Between weeks 10-13
What should normal nuchal translucency be?
The transvaginal ultrasound measures the fetal nuchal translucency (NT), which should be less than 3 mm.
What is an abnormal nuchal translucency?
If there is a defect in the skin or spinal cord, the NT measurement will be increased. All cases of anencephaly can be diagnosed with this test alone. This is the earliest noninvasive way of catching Down syndrome but requires a specialized ultrasonographer.
What are the components of the quadruple screen?
BetaHCG, AFP, Estriol, and Inhibin A
What do we observe in the quad screen in down syndrome?
Increasned HCG, decreased AFP and estriol, increased inhibin A
When is quad screening conducted?
best time is 16–18 weeks, early in the second trimester
What happens to AFP in neural tube defects?
AFP is elevated when there are open neural tube defects.
This screen can also assess for neural tube defects, such as spina bifida spectrum disorders.
What ethnicity specific screenings do we do?
Caucasians are screened for cystic fibrosis, Ashkenazi Jews are screened for Tay-Sachs, and African Americans are screened for the sickle cell trait (mom). Ethnicity-specific testing can be offered to all patients in the first trimester, but appropriate counseling should be offered (positive and negative predictive values are affected by the prevalence of disease, so testing is less accurate in low-risk populations).
