Nursing 209

N209: Reproductive Health Study Guide

3.8 Diagnostic Testing First Trimester Testing • Pregnancy confirmation o Tests for presence of hCG (human chorionic gonadotropin) o hCG cannot be detected until implantation occurs (about 10 days after conception) o Levels double approximately every 36 hours and peak at 10 weeks gestation (100,000) o Urine: Done via home test or in a physician’s office; depends upon sensitivity, but these tests are usually accurate two weeks after conception o Blood: Earlier detection than urine; approximately 10 days after conception o Quantitative: Beta hCG measures exact level in blood o Qualitative: Tests only for presence of hCG in urine • Ultrasound o Differentiates between normal (intrauterine) and abnormal (ectopic or molar) pregnancy o Transvaginal approach allows for early pregnancy detection at 4-5 weeks gestation First Trimester Screening • Sequential screen: Non-invasive screening (not diagnostic, it determines risk only) for genetic or chromosomal defects performed between 11-13.6 weeks gestation o Part 1: Consists of a blood test and ultrasound  Blood test: Concentration of PAPP-A (pregnancy associated plasma protein) and free B-hCG  Ultrasound: Looks for presence of nasal bone and measures nuchal translucency (fluid- filled area in the back of the fetal neck; greater in affected pregnancies)  If the screen in positive, the second stage is skipped and the patient is offered further diagnostic testing o Part 2: Blood sample done between 15-21 weeks (quad screen)  Four markers: AFP, total B-hCG, unconjugated Estriol (uE3), and Inhibin A  Results: If lower than 1:270 after part 2, it is considered negative for Down Syndrome (but does not rule out the possibility)  Positive if greater than or equal to 1:30 in Part 1 • Non-invasive prenatal testing (NIPT) o Analyzes cell-free DNA in maternal blood o Can be done any time after 10 weeks gestation; usually done up to 22 weeks o Used as a follow-up test for first or second trimester screening o Currently not recommended for low risk women o Recognized by ACOG as a primary screening test for the following:  35 years or older at time of delivery  Abnormal ultrasound finding, indicating increased risk for aneuploidy

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