Abstract
Objective: To demonstrate the differences in intrauterine fetal deaths and neonatal deaths between small for date (SFD) and Non-SFD neonates by applying a novel classification from both Z scores of placental weight (PW) and fetal/placental weight ratio (F/P) to small for gestational age (SGA) neonates. Methods: From 93,034 placentas/infants of mothers who vaginally delivered a singleton infant (Japan Perinatal Registry Network database 2013), SGA (n=7,780) was chosen according to the reference to Japanese neonatal growth chart. They were divided into two subgroups: SFD (body weight and height less than the 10(th) percentile, n=3,379) and Non-SFD (only body weight less than the 10(th) percentile, n=4,401). Z scores of PW and F/P based on the standard curves for sex-, parity-, and gestational-age-specific PW and F/P were calculated. The population was classified into 9 groups according to the combination of 'low vs. middle vs. high' i) PW Z score and ii) F/P Z score. In both i) and ii), ± 1.28 standard deviations in the Z scores were used for classifying low vs. middle vs. high, with 3×3 making 9 groups. From top-left to bottom-right, we labeled the groups as Group A to Group I. Results: SFD and Non-SFD neonates distributed in the same 6 groups (A, D, E, G, H, I). In group E, which was considered to be balanced placental and infant growth, the incidence of intrauterine fetal death was significantly higher in Non-SFD neonates than in SFD neonates. In group D, which was considered to be small placenta and balanced infant growth, the incidence of neonatal death was significantly higher in SFD neonates than in Non-SFD neonates. Conclusion: Assessment of SGA neonates by dividing them into SFD and Non-SFD neonates and application of a 9-group classification by PW and F/P Z scores were informative to understand the pathophysiological involvement of an imbalance between placental and fetal sizes.