A global reference for fetal-weight and birthweight percentiles

Area of Science:

• Perinatal health research
• Biostatistics
• Global public health

Background:

• Defining small for gestational age (SGA) globally is challenging due to limitations in existing birthweight references, particularly for preterm births and diverse populations.
• Ultrasound-derived references may lack universal applicability, while individualized references can be too complex for resource-limited settings.
• Existing methods struggle to provide accurate SGA assessments across varied global populations.

Purpose of the Study:

• To develop a generic fetal weight and birthweight reference that is easily adaptable to local populations worldwide.
• To overcome the deficiencies of existing non-customized and individualized SGA references.
• To create a practical and accurate tool for identifying SGA infants in diverse global settings.

Main Methods:

• A generic fetal weight reference was created by adjusting Hadlock's reference using Gardosi's proportionality concept, allowing local adaptation based on mean 40-week birthweight.
• Data from 237,025 births across 24 countries in Africa, Latin America, and Asia (WHO Global Survey on Maternal and Perinatal Health) were used for validation.
• Multilevel logistic regression analyzed the odds ratio (OR) of adverse perinatal outcomes for SGA infants compared to non-SGA infants, using three reference types: non-customized, country-specific, and individualized.

Main Results:

• The country-specific reference showed a significantly higher odds ratio (OR) for adverse outcomes in SGA infants (2.87) compared to the non-customized Hadlock reference (1.59).
• The fully individualized reference also demonstrated a high OR for adverse outcomes (2.84), comparable to the country-specific reference.
• The developed generic reference, when adapted to country-specific data, demonstrated a strong association with adverse perinatal outcomes.

Conclusions:

• The proposed generic reference for fetal and birthweight percentiles is easily adaptable to local populations, enhancing its global utility.
• This adaptable reference demonstrates superior ability in predicting adverse perinatal outcomes compared to non-customized references.
• The method offers a simpler alternative to fully individualized references without compromising predictive accuracy, making it suitable for diverse healthcare settings.