| name | design-prenatal-genetic-screening-plan |
| description | Use when planning genetic testing during pregnancy — e.g., "what genetic tests during pregnancy", "NIPT vs amniocentesis", "anatomy scan timing", "Down syndrome screening options" |
| source | ACOG Practice Bulletin 226 (2021); ACOG Committee Opinion 693 (2017, cfDNA); SMFM Consult Series 2015; ACMG Guidelines Prenatal Diagnosis 2016 |
| tags | ["pregnancy","genetic-screening","NIPT","amniocentesis","chromosomal","anatomy-scan","health"] |
| verified | true |
Design Prenatal Genetic Screening Plan
Map the sequence of genetic screening and diagnostic options across pregnancy.
Why This Is Best Practice
Adopted by: ACOG, SMFM, ACMG — offer all pregnant patients the full menu of screening/diagnostic options at the first visit.
Impact: cfDNA/NIPT detects trisomy 21 with 99% sensitivity and 99.9% specificity (Palomaki et al., Genet Med 2011) vs. 80% for serum quad screen. Structured genetic counseling increases informed decision-making and reduces unnecessary invasive testing (Bernhardt et al., 2013).
Why best: Patients cannot make informed decisions without a structured menu. Timing windows are narrow — missing them forecloses options.
Steps
- Counseling at first visit (weeks 8–10): offer all options; document patient's decision.
- First trimester screening (weeks 10–13):
- cfDNA/NIPT: screens for trisomy 21, 18, 13, sex chromosome aneuploidies; can determine fetal sex
- Best for: everyone; especially accurate for trisomy 21
- Limitation: screening only, not diagnostic; high BMI may cause test failure
- Nuchal translucency ultrasound (NT): NT >3.5 mm = elevated risk for chromosomal/cardiac anomalies
- First trimester serum screen (PAPP-A + free βhCG): combined with NT for integrated risk score
- Second trimester (weeks 15–20):
- Quad screen (AFP, hCG, estriol, inhibin A): if NIPT declined or unavailable; detects ~80% of Down syndrome
- Anatomy ultrasound (18–20 weeks): structural survey — brain, spine, heart, face, limbs; cervical length
- Diagnostic testing — offer if screening positive, advanced maternal age (≥35), or patient preference:
- CVS (chorionic villus sampling): weeks 10–13; 1 in 300–500 miscarriage risk; provides diagnosis
- Amniocentesis: weeks 15–20; 1 in 300–500 miscarriage risk; diagnoses chromosomal and single-gene disorders
- GBS screen (weeks 35–37): rectal-vaginal swab (see design-group-b-strep-protocol).
- Document: all offered tests, patient decisions, and results in the chart.
Rules
- NIPT is screening, not diagnostic — a positive result requires confirmation with amniocentesis before any irreversible decision.
- Advanced maternal age (≥35) increases aneuploidy risk but is not by itself an indication for invasive testing.
- Carrier screening (cystic fibrosis, spinal muscular atrophy, hemoglobinopathies) is separate from aneuploidy screening — offer preconception or at first visit.
Examples
Low-risk 28-year-old: NIPT at 12 weeks → anatomy scan at 19 weeks → GBS at 36 weeks.
High-risk (prior trisomy 21, age 38): NIPT + NT at 12 weeks; consider amniocentesis; detailed anatomy scan at 20 weeks; echocardiogram at 22 weeks.
Common Mistakes
- Ordering NIPT at 8 weeks — too early; fetal fraction insufficient before 10 weeks.
- Assuming NIPT covers all genetic conditions — it screens aneuploidy only; does not diagnose single-gene disorders.
- Skipping anatomy scan because NIPT was negative — NIPT does not detect structural anomalies.
Health Disclaimer: Genetic screening decisions are deeply personal and involve complex medical, ethical, and personal considerations. Genetic counseling is strongly recommended before any diagnostic procedure.
