## **Core Concept**
The World Health Organization (WHO) defines low birth weight (LBW) based on the infant's weight at birth. This classification is crucial for identifying newborns at higher risk of health and developmental issues. Low birth weight is a significant public health concern globally.

## **Why the Correct Answer is Right**
The correct definition of low birth weight, as per the WHO, is a birth weight of less than 2,500 grams. This threshold is used internationally to categorize newborns who may require special care and monitoring due to their increased risk of complications. The 2,500-gram cutoff is based on evidence showing that babies born below this weight have higher risks of mortality and morbidity.

## **Why Each Wrong Option is Incorrect**
- **Option A:** [Weight less than 2,000 grams] - This is too low; it represents very low birth weight, a subset of low birth weight.
- **Option B:** [Weight less than 3,000 grams] - This is not the correct threshold; it's higher than the WHO-defined low birth weight.
- **Option C:** [Weight less than 1,500 grams] - This represents very low birth weight, which is a more severe category.
- **Option D:** [Weight less than 2,500 grams] - This is the correct definition.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that low birth weight is defined as less than 2,500 grams by the WHO. Babies with low birth weight are at a higher risk for health problems and may need close monitoring. This definition helps in planning healthcare interventions.

## **Correct Answer:** . 2500 grams