A 28-year-old primigravida at 20 weeks gestation attends her routine antenatal clinic visit. Regarding the investigations and assessments recommended at this gestational age, all of the following are standard EXCEPT:

Explanation

## Antenatal Investigations at 20 Weeks Gestation ### Timing of Key Investigations in Pregnancy **Key Point:** The 20-week visit is the second trimester milestone visit, with specific investigations appropriate to this gestational age. GDM screening is performed later (24–28 weeks), not at 20 weeks. ### Standard Investigations at 20 Weeks | Investigation | Purpose | Gestational Age | | --- | --- | --- | | Detailed anatomical ultrasound | Assess fetal anatomy, detect structural defects, confirm placental location | 18–22 weeks | | Maternal serum screening (triple/quadruple) | Screen for Down syndrome, Edwards syndrome, Patau syndrome | 15–22 weeks | | Blood pressure & urinalysis | Screen for hypertension, proteinuria, preeclampsia risk | Every visit | | OGTT / fasting glucose | Screen for gestational diabetes mellitus | 24–28 weeks | ### Why GDM Screening is NOT at 20 Weeks **High-Yield:** Gestational diabetes screening is performed at **24–28 weeks gestation**, not at 20 weeks. This is the standard window across ICMR, WHO, and ACOG guidelines. Screening at 20 weeks is not recommended in routine low-risk pregnancies. **Mnemonic:** **GDSW** = Gestational Diabetes Screening at Week 24–28 (not 20). **Clinical Pearl:** Early fasting glucose at the first visit may identify pre-existing diabetes, but the formal OGTT for GDM is deferred to the second-trimester screening window (24–28 weeks) to allow adequate time for metabolic adaptation and to optimize sensitivity. ### What IS Done at 20 Weeks 1. **Detailed fetal anatomy scan** — assess all organ systems, rule out major structural defects 2. **Maternal serum screening** — triple marker (AFP, hCG, uE3) or quadruple marker (adds inhibin A) 3. **Vital signs & urinalysis** — ongoing surveillance 4. **Fundal height measurement** — assess growth trajectory ### Summary Options 0, 1, and 3 are all appropriate at 20 weeks. Option 2 (OGTT/fasting glucose for GDM) is NOT standard at this gestation — it belongs at 24–28 weeks. [cite:Williams Obstetrics 26e Ch 9; ICMR Antenatal Care Guidelines; ACOG Practice Bulletin #229]