A 6-month-old infant is referred to the growth clinic because his weight gain has slowed significantly over the past 2 months. Birth weight was 3.2 kg, and at 3 months he weighed 5.8 kg. Current weight is 6.5 kg (below 5th percentile for age), and length is 63 cm (3rd percentile). Head circumference is 41 cm (10th percentile). The infant is exclusively breastfed and appears clinically well with normal developmental milestones. Which investigation is most appropriate to assess the adequacy of milk transfer and rule out breastfeeding-related failure to thrive?

Explanation

## Assessment of Breastfeeding Adequacy in Failure to Thrive **Key Point:** Test weighing (pre- and post-feed infant weight measurement) is the gold standard, non-invasive investigation to quantify milk transfer during breastfeeding and identify inadequate intake as the cause of poor weight gain. ### What Is Test Weighing? Test weighing involves: 1. Weighing the infant before the breastfeed (using a calibrated electronic scale, accurate to ±2 g). 2. Allowing the infant to breastfeed ad libitum. 3. Weighing the infant immediately after the feed (without changing diaper). 4. The difference in weight equals the volume of milk transferred (1 g ≈ 1 mL). 5. Repeating over 24 hours (typically 3–4 feeds) to calculate average milk intake. ### Interpretation | Average Milk Transfer per Feed | Clinical Significance | |--------------------------------|----------------------| | **> 50 mL** | Adequate milk transfer | | **30–50 mL** | Borderline; assess latch and feeding frequency | | **< 30 mL** | Inadequate; intervention needed (latch correction, supplementation) | **Clinical Pearl:** Test weighing is superior to maternal perception of milk transfer; many mothers incorrectly believe they are producing insufficient milk when the problem is actually latch or feeding technique. **High-Yield:** Test weighing is non-invasive, repeatable, and provides immediate quantitative data without radiation or blood draws — making it the first-line investigation for suspected breastfeeding failure to thrive. ### Why Other Investigations Are Secondary - **Serum albumin/prealbumin:** These assess nutritional status *after* poor intake has caused protein depletion; they do not identify the *cause* of inadequate intake. - **Dietary recall:** Maternal nutrition is important for milk quality, but does not directly measure milk transfer to the infant. - **Breast ultrasound:** Not a standard diagnostic tool for assessing milk transfer; structural abnormalities are rare and do not explain most cases of inadequate transfer. [cite:Nelson Textbook of Pediatrics 21e Ch 9]