//fpnotebook.com/
Antenatal Screening
Aka: Antenatal Screening, Prenatal Diagnosis
- See Also
- Aneuploidy Screening
- First Trimester Education
- Pregnancy Risk Assessment
- Placental Cell-Free DNA
- Trisomy Findings on Fetal Ultrasound
- Nuchal Translucency
- Second Trimester Ultrasound
- Epidemiology
- Aneuploidy (chromosomal abnormalities) affect one in 150 pregnancies
- Result in 50% of pregnancy losses
- Children with intellectual and physical Disability
- Aneuploidy risk increases with maternal age (mean maternal age has increased over time)
- Overall risk (Trisomy 13, Trisomy 18, Trisomy 21)
- Age 35 year old Risk: 1 per 200 pregnancies
- Age 45 year old Risk: 1 per 20 pregnancies
- Down Syndrome (Trisomy 21)
- Age 20 years old: 1 per 1480
- Age 40 years old: 1 per 85
- Precautions: Counseling
- See First Trimester Education
- Discuss a patient's overall risk of a child with Fetal Aneuploidy
- See Pregnancy Risk Assessment
- Discuss the types of tests available (as appropriate to patient risk)
- Give Patient Education (see resources below)
- See testing options (below)
- Review risks and benefits of testing
- False Positive Tests
- False Positive tests are common, as cut-offs favor higher Test Sensitivity
- Associated with increased parental anxiety
- Risk of additional testing (e.g. Amniocentesis)
- False Negative Tests
- False Negative tests are less common, as a negative test has high NPV in Aneuploidy testing
- However, in high risk patients (e.g. advanced maternal age), noninvasive tests may be inadequate alone
- Multiple Gestation Pregnancies
- Exercise caution for interpretation in Twin Gestation
- Serum testing is unreliable in triplets and higher
- Ultrasound for Nuchal Translucency and Fetal Survey are better screening tools in this cohort
- Diagnostics: Available Tests
- Ultrasound
- First Trimester Ultrasound (Nuchal Translucency)
- Second Trimester Ultrasound (Fetal Survey)
- See Aneuploidy Markers on Second Trimester Ultrasound
- Labs
- Pregnancy-Associated Plasma Protein A (PAPP-A) and bHCG (Free or Total) at 10 to <14 weeks
- Quadruple Screening (Alpha Fetoprotein, Unconjugated Estriol, Free bHCG, Inhibin A) at 15 to <23 weeks
- Placental Cell-Free DNA (Noninvasive Prenatal Testing or NIPT) after 10 weeks gestation
- Invasive Tests
- Chorionic Villus Sampling (10-13 weeks)
- Risk of pregnancy loss: 1 in 455 (0.2%)
- Amniocentesis (15-18 weeks)
- Risk of pregnancy loss: 1 in 900 (0.1%)
- Preimplantation Genetic Screening (In-Vitro Fertilization)
- Preimplantation Genetic Screening is performed with in-vitro fertilization before Embryo implantation
- Cell biopsy has a risk of False Positive and False Negative
- Occurs due to mosaicism in which Chromosomes are from pre-placental tissue no found in Embryo
- Does not replace antenatal Aneuploidy Screening
- Approach: Testing Protocols
- See Placental Cell-Free DNA
- First Trimester Combined Screening (at 10 to <14 weeks)
- Nuchal Translucency
- Pregnancy-Associated Plasma Protein A (PAPP-A) AND
- bHCG (Free or Total)
- Second Trimester Quad Screening (at 15 to <23 weeks)
- Alpha Fetoprotein (aFP)
- Unconjugated Estriol (uE3)
- Free bHCG
- Inhibin A
- Second Trimester Fetal Survey
- See Aneuploidy Markers on Second Trimester Ultrasound
- Trisomy 21 Test Sensitivity: 50-60%
- Least accurate screening for Aneuploidy
- Follow positive Ultrasound testing with Second Trimester Quad Screening or Placental Cell-Free DNA
- Integrated Screening
- First Trimester Combined Screening (PAPP-A, bHCG, Nuchal Translucency) at 10 to <14 weeks AND
- Second Trimester Quad Screening (aFP, uE3, bHCG, Inhibin A) at 15 to <23 weeks
- Trisomy 21 Test Sensitivity: 96%
- Wald (1999) N Engl J Med 341(7): 461-7 [PubMed]
- Serum Integrated Screening
- First Trimester Combined Screening (PAPP-A, bHCG) WITHOUT Nuchal TranslucencyUltrasound AND
- Second Trimester Quad Screening (aFP, uE3, bHCG, Inhibin A) at 15 to <23 weeks
- Trisomy 21 Test Sensitivity: 88%
- Stepwise Sequential Screening
- First Trimester Combined Screening (PAPP-A, bHCG, Nuchal Translucency) at 10 to <14 weeks
- Screening Results in combination with Pregnancy Risk Assessment inform decision making
- Lower Risk
- Second Trimester Quad Screening (aFP, uE3, bHCG, Inhibin A) at 15 to <23 weeks
- Higher Risk
- Consider Placental Cell-Free DNA
- Invasive Testing (Chorionic Villus Sampling or Amniocentesis)
- Trisomy 21 Test Sensitivity: 95%
- Benn (2007) Am J Obstet Gynecol 197(3): 312e1-5 [PubMed]
- Contingent Sequential Screening
- First Trimester Combined Screening (PAPP-A, bHCG, Nuchal Translucency) at 10 to <14 weeks
- Screening Results in combination with Pregnancy Risk Assessment inform decision making
- Low Risk (81% of results)
- No further testing
- Intermediate Risk (18% of results)
- Consider Placental Cell-Free DNA
- Second Trimester Quad Screening (aFP, uE3, bHCG, Inhibin A) at 15 to <23 weeks
- High Risk (1% of results)
- Invasive Testing (Chorionic Villus Sampling or Amniocentesis)
- Trisomy 21 Test Sensitivity: 85-88%
- Wright (2004) Prenat Diagn 24(10): 762-66 [PubMed]
- Resources: Patient Education
- Making decisions about screening for Down Syndrome in pregnancy
- https://www.psychosocialresearchgroupunsw.org/decision-aids.html
- Cell-Free DNA (ACOG)
- https://www.acog.org/patient-resources/infographics/cell-free-dna-prenatal-screening-test
- Prenatal Genetic Testing
- https://www.acog.org/patient-resources/infographics/prenatal-genetic-testing-chart
- References
- (2016) Obstet Gynecol 127(5): e123-37 [PubMed]
- Anderson (2009) Am Fam Physician 79(2): 117-23 [PubMed]
- LeFevre (2020) Am Fam Physician 101(8):481-8 [PubMed]