A 28-year-old primigravida at 20 weeks of gestation attends her antenatal clinic. Regarding the investigations and counselling she should receive at this visit, all of the following are appropriate EXCEPT:

Explanation

## Second Trimester Screening at 20 Weeks: What is Appropriate ### Standard Investigations at 20-Week Antenatal Visit **Key Point:** At 20 weeks, the focus is on **detailed anatomical assessment** and **ongoing screening for complications**. Serum screening for aneuploidy should have been done earlier (first trimester or early second trimester), not at 20 weeks. ### Why AFP Alone at 20 Weeks is INAPPROPRIATE **High-Yield:** Maternal serum screening for chromosomal abnormalities follows a **specific timing protocol**: | Screening Method | Optimal Timing | Components | Detection Rate | |---|---|---|---| | **Combined screening** | 11–14 weeks | PAPP-A + β-hCG + NT ultrasound | 90% for Down syndrome | | **Triple screen** | 15–20 weeks | AFP + hCG + uE3 | 70% for Down syndrome | | **Quadruple screen** | 15–20 weeks | AFP + hCG + uE3 + inhibin A | 80–85% for Down syndrome | | **AFP alone** | Any time | Single marker only | <50% detection — INADEQUATE | **Clinical Pearl:** AFP alone is **not a validated screening test** for aneuploidy. It must be combined with hCG and uE3 (triple screen) or with hCG, uE3, and inhibin A (quadruple screen) to have acceptable detection rates. Using AFP alone is **outdated and ineffective**. **Warning:** If serum screening was not done in the first trimester (11–14 weeks), a triple or quadruple screen can still be offered at 15–20 weeks. But AFP in isolation is never appropriate for Down syndrome screening. ### What IS Appropriate at 20 Weeks 1. **Clinical examination:** - Fundal height measurement (assess growth) - Blood pressure (screen for hypertension) - Urinalysis (screen for proteinuria/preeclampsia) - Fetal heart rate assessment (viability, rate) 2. **Ultrasound:** - **Level II (detailed) anatomy scan** — the hallmark of the 20-week visit - Fetal biometry - Amniotic fluid volume - Placental location - Screen for structural anomalies (cardiac, neural tube, renal, limb, etc.) 3. **Biochemical screening (if not done earlier):** - Triple or quadruple screen (NOT AFP alone) - NIPT (if available and desired) ### Summary: What Fits at 20 Weeks | Appropriate | NOT Appropriate | |---|---| | Fundal height measurement | AFP alone for aneuploidy screening | | Fetal heart rate by Doppler | Amniocentesis without indication | | Detailed anatomy ultrasound | Routine glucose tolerance test (done at 24–28 weeks) | | BP + urinalysis | Serology (done at first visit) | | Triple/quadruple screen (if not done earlier) | — |