Diagnostic test characteristics of placental weight in the prediction of small-for-gestational-age neonates

OBJECTIVE: To assess the diagnostic test characteristics of placental weight as a clinical predictor of small-for-gestational-age (SGA) neonates. STUDY DESIGN: Placentas were weighed at 45,846 deliveries. Predictive values and likelihood ratios (LRs) were calculated assessing placental weight (lowest tertile vs. top 2 or mid/high tertiles) as a predictor of SGA both overall and by maternal age, gestational age, maternal weight, reported early pregnancy smoking, race, neonatal sex and parity. RESULTS: Although the positive predictive value (PPV) of low placental weight was poor (0.19), the negative predictive value (NPV) was high (0.97). Both NPV and LR- were powerfully predictive in women at earlier gestational ages. At gestational ages <32 weeks, LR-was 0.11, showing that among women with mid/high placental weight, the proportion with SGA (false negative) was about 1/10 that without SGA (true negative). CONCLUSION: Placental weight in the mid or upper tertile has strong NPV and LR- for delivery of an SGA neonate. Further study of the value of placental size in prediction of SGA is warranted.