Term and preterm (<34 and <37 weeks gestation) placental pathologies associated with fetal growth restriction.

Objective: The present study was aimed to compare term versus preterm placental pathologies associated with fetal growth restriction (FGR).
Study Design: A retrospective cohort study was performed, including all singleton deliveries of FGR with placental pathology examination. Comparison of placental findings was performed between neonates who were born at term versus preterm. Preterm was defined as <37 completed weeks of gestation, and <34 weeks gestation in another analysis. When one or more of the following pathology was found in microscopic examination of the placental tissue, the term uteroplacental insufficiency was defined: placental infarct, fibrosis of chorionic villi, thickening of blood vessels and poor vascularity of the chorionic villi.
Results: Macroscopic placental findings were available for 1,104 singleton FGR neonates; of these, 395 placentas had microscopic examinations. A significant greater proportion of preterm FGR cases had pathology findings associated with uteroplacental insufficiency as compared to term FGR (29.4 vs. 36.7%; OR = 1.4 95%, CI = 1.05-1.9; P = 0.019). The same pattern was seen while comparing placentas of FGR neonates who were born before and after 34 weeks (32.4 vs. 39.4%; OR = 1.4, 95% CI 1.02-1.8; P = 0.028). Syncytial knots were significantly more common in placentas from neonates who were delivered before 34 weeks of pregnancy (15.2 vs. 6.3%; OR = 2.6, 95% CI 1.3-5.6; P = 0.005). This trend was not statistically significant while comparing FGR before and after 37 weeks gestation (10.9 vs. 4.6%; OR = 2.4, 95% CI 0.99-7.7; P = 0.052). Meconial impregnation was more common among term versus preterm FGR neonates <37 weeks (22.4% vs. 7.2% OR = 3.7, 95% CI 2.3-5.9; P < 0.001), as well as among neonates who were born before and after 34 weeks of gestation (14.5 vs. 5.9%; OR = 0.4, 95% CI 0.2-0.6; P < 0.001).
Conclusions: Placentas of preterm FGR neonates (either <37 weeks or <34 weeks gestation) reveal numerous pathologies reflecting uteroplacental insufficiency and abnormal blood supply. The presence of increased syncytial knots in preterm FGR neonates is probably due to exposure to hypoxia and reactive oxygen agents.