The placental factor in spontaneous preterm birth in twin vs. singleton pregnancies

The association between infection and inflammatory response in singleton preterm birth (PTB) is well established, yet, less is known about PTB in twins. We aimed to compare the placental component and pregnancy outcome in pregnancies complicated with PTB of singletons vs. twin deliveries. We hypothesized that due to different underlying mechanisms, placental inflammatory lesions will be more prevalent in placentas derived from singleton pregnancies than twins.

Labor characteristics, neonatal outcome and placental histopathology reports of spontaneous PTB at 24-33⁶/₇ weeks, from 1/2008-12/2015, were reviewed.

were compared between dichorionic-diamniotic twin deliveries (twins group) and singleton deliveries (singleton group) matched for gestational age. Excluded from the study medically indicated deliveries, due to preeclampsia or fetal growth restriction, and monochorionic twins. Placental lesions were classified to maternal vascular supply lesions, fetal vascular supply lesions, and maternal (MIR) and fetal (FIR) inflammatory responses. Composite neonatal outcome was defined as one or more of early complications: respiratory distress, necrotizing enterocolitis, sepsis, blood transfusion, ventilation, seizures, intra-ventricular hemorrhage, hypoglycemia, phototherapy, or death.

The twins group (n=72) was characterized by higher maternal BMI (p=0.009), and higher rates of assisted reproductive techniques (56.2% vs. 17.8%, p<0.001) and cesarean deliveries (75.3% vs. 32.8%, p<0.001) as compared to the singleton group (n=72). Placentas from the singleton group were characterized by higher rate of MIR, 58.9% vs. 19.2%, (p<0.001), FIR, 31.5% vs. 3.4%, (p<0.001), retro-placental hemorrhage, 26% vs. 8.9% (p<0.001), and vascular lesions related to maternal malperfusion, 28.8% vs. 9.6%, (p<0.001), as compared to placentas from the twins group. Higher rate of neonatal sepsis was observed in the singleton group as compared to the twins group, 24.7% vs. 4.1%, p<0.001, respectively. By logistic regression analyses retro-placental hemorrhage, placental maternal vascular malperfusion lesions, MIR, FIR and neonatal sepsis were found to be independently associated with singleton PTB: aOR 3.4, 95% CI 2.1-6.9, p<0.001, aOR=3.1, 95% CI 1.8-7.2, p<0.001, aOR=2.9, 95% CI 1.4-7.8, p<0.001, aOR=4.9, 95% CI 2.3-6.9, p<0.001, and aOR=4.8, 95% CI 2.3-6.7, p<0.001 respectively.

Placentas from singleton PTBs are characterized by higher rate of inflammatory and malperfusion lesions. The lack of these findings in twins PTBs suggests different factors that participate in the development of preterm birth in twins, such as over-distension of the uterus and up regulation of oxytocin receptors.