The differences in placental pathology and neonatal outcome in singleton vs. twin gestation complicated by small for gestational age

Objective: We aimed to compare placental histopathology and neonatal outcome between dichorionic diamniotic (DCDA) twins and singleton pregnancies complicated by small for gestational age (SGA). Methods: Medical files and placental pathology reports from all deliveries between 2008 and 2017 of SGA neonates, (birthweight < 10th percentile), were reviewed. Comparison was made between singleton pregnancies complicated with SGA (singletons SGA group) and DCDA twin pregnancies (Twins SGA group), in which only one of the neonates was SGA. Placental diameters were compared between the groups. Placental lesions were classified into maternal and fetal vascular malperfusion lesions (MVM and FVM), maternal (MIR) and fetal (FIR) inflammatory responses, and chronic villitis. Neonatal outcome parameters included composite of early neonatal complications. Results: The twins SGA group (n = 66) was characterized by a higher maternal age (p = 0.011), lower gestational age at delivery (34.9 ± 3.1 vs. 37.7 ± 2.6 weeks, p < 0.001), and a higher rate of preeclampsia (p = 0.010), compared to the singletons SGA group (n = 500). Adverse composite neonatal outcome was more common in the twins SGA group (p < 0.001). Placental villous lesions related to MVM (p < 0.001) and composite MVM lesions (p = 0.04) were more common in the singletons SGA group. On multivariate logistic regression analysis, the singletons SGA group was independently associated with placental villous lesions (aOR 3.6, 95% CI 1.9–7.0, p < 0.001) and placental MVM lesions (aOR 2.44, 95% CI 1.29–4.61, p = 0.006). Conclusion: Placentas from SGA singleton pregnancies have more MVM lesions as compared to placentas from SGA twin pregnancies, suggesting different mechanisms involved in abnormal fetal growth in singleton and twin gestations.