Customized criteria for fetal growth predictive of neonatal outcomes

1. Infants classified as small for gestational age (SGA) by INTERGROWTH-21 and customized criteria were more likely to experience stillbirth, neonatal morbidity and death.

2. Infants classified as SGA by INTERGROWTH-21 criteria alone was not associated with increased risk for adverse outcomes.

Evidence Rating Level: 2 (Good)

Study Rundown: Growth restriction occurs when a fetus has not reached its expected growth and can occur as a result of fetal, placental and/or maternal factors. While SGA is defined as birth weight below the 10th percentile for gestational age, this definition does not distinguish between infants who are constitutionally small and those that are growth-restricted. This distinction is clinically significant, as infants with fetal growth restriction are at greater risk for premature delivery, impaired thermoregulation, neonatal death, as well as growth and neurodevelopmental abnormalities. INTERGROWTH-21 is a growth standard that has been used in multiple countries and posited by researchers and clinicians as a useful tool in the assessment of infant anthropometrics. In the present work, the authors evaluated the ability of INTERGROWTH-21 compared to customized standards for SGA to identify infants at risk for adverse outcomes. They found that classification as SGA by either customized standards alone or using both standards was associated with increased risk for adverse perinatal outcomes. Classification as SGA by INTERGROWTH-21 criteria alone was not associated with increased risk for adverse outcomes.

Strengths of the study were large population-based data and comparison of INTERGROWTH-21 criteria to a standard model. The study was limited by post-hoc analysis and limited generalizability to populations of different ethnic composition. Further evaluation of INTERGROWTH-21 in prospective studies is needed to clarify its role in predicting adverse perinatal outcomes.

Click to read the study in AJOG

Relevant Reading: Small for gestational age infants classified by customized or population birthweight centiles: impact of gestational age at delivery

In-Depth [prospective cohort]: This secondary analysis of prospectively collected population-based data compared the ability of the INTERGROWTH-21 criteria and customized standards for SGA to predict perinatal outcomes in over 53,000 singleton pregnancies. Factors included in the customized standards model were maternal height, weight, parity, ethnicity and infant sex. The primary outcomes of interest were stillbirth, neonatal death, and neonatal morbidity.

Infants classified as SGA by both criteria were most likely to experience neonatal death or morbidity (RR 4.1, CI 3.7-4.6) and stillbirth (RR 8.3, CI 5.1-13.4). Infants classified as SGA by customized criteria alone experienced a lesser increased risk of (RR 2.0, CI 1.8-2.2) and stillbirth (RR 3.0, CI 1.7-5.3) while those classified as SGA by INTERGROWTH-21 criteria alone did not experience increased risks of adverse outcomes. Sensitivity and specificity of INTERGROWTH-21 were 14.3% and 96.1% respectively compared to 26.6% and 89.2% with the customized standard.

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