Are the findings of an intervillous thrombus, increased syncytial knots, focally increased perivillous fibrin, and acute chorionitis in a term placenta (third trimester placenta) normal?

Assessment of Term Placenta Findings

Most of these findings represent normal variants or common incidental findings in term placentas, with the critical exception of acute chorionitis, which is always pathologic and indicates maternal-fetal infection.

Individual Finding Analysis

Intervillous Thrombus (1 cm)

• Small intervillous thrombi are common incidental findings in term placentas and typically have no clinical significance when measuring 1 cm 1
• Intervillous thrombi are listed among the placental pathologic findings associated with basal plate myometrial fibers (BPMF), suggesting they can occur in various placental conditions 1
• A 1 cm thrombus falls within the range of clinically insignificant findings that do not affect maternal or fetal outcomes 1

Increased Syncytial Knots

• Increased syncytial knots are a hallmark feature of maternal vascular malperfusion (MVM) and represent syncytiotrophoblast stress rather than a normal finding 2
• The American Heart Association notes that syncytiotrophoblast stress manifests as increased syncytial knots in both early-onset and term preeclampsia, reflecting a placenta that has reached the limits of its functional reserves 2
• These findings should prompt correlation with clinical risk factors including hypertensive disorders, fetal growth restriction, and adverse pregnancy outcomes 2
• Increased syncytial knots are associated with multiple placental pathologies including decreased placental weight, abnormal uteroplacental vessels, villous agglutination, increased perivillous fibrin, and infarction 2
• In COVID-19 infected placentas, features of maternal vascular malperfusion such as increased syncytial knots were present in 100% of cases 3

Focally Increased Perivillous Fibrin

• Focal perivillous fibrin deposition is a common finding that can be seen in association with maternal vascular malperfusion 1
• Increased perivillous fibrin is listed among placental pathologic findings associated with BPMF and can occur with increased syncytial knots 1
• In COVID-19 infected placentas, increased focal perivillous fibrin depositions were present in 37.7% of cases 3
• The key distinction is between focal versus massive perivillous fibrin deposition (MPVFD), which requires fibrin extending over at least 25% of placental volume and is associated with severe adverse outcomes including recurrent miscarriage, IUFD, IUGR, and preterm delivery 4
• Focal findings are generally of limited clinical significance unless part of a broader pattern of maternal vascular malperfusion 2

Acute Chorionitis

• Acute chorionitis is NEVER a normal finding and always indicates maternal-fetal infection 5
• This represents ascending bacterial infection from the maternal genital tract and is a component of chorioamnionitis 5
• Clinical correlation is essential to assess for maternal fever, prolonged rupture of membranes, and neonatal sepsis risk 5
• The presence of acute chorionitis may explain pathophysiologic changes including potential fetal hypoxia and requires neonatal evaluation for infection 5

Clinical Significance and Integration

The Pattern Matters

• The combination of increased syncytial knots and increased perivillous fibrin suggests maternal vascular malperfusion as an underlying pathophysiologic process 2
• This pattern should prompt review of maternal conditions including hypertensive disorders, diabetes, or other vascular complications 2
• The placental weight of 449 g should be evaluated against gestational age-specific reference values, as decreased placental weight is associated with maternal vascular malperfusion 2

Critical Action Items

• The acute chorionitis requires immediate clinical correlation regarding maternal infectious risk factors and neonatal infection evaluation 5
• Document whether the neonate received appropriate sepsis evaluation and antibiotic coverage if indicated 5
• Quantitative documentation of syncytial knots compared to gestational age-specific reference values is important for accurate diagnosis 2
• Recognize increased syncytial knots as a marker of uteroplacental malperfusion that may have contributed to adverse pregnancy outcomes 2

Future Pregnancy Implications

• The presence of increased syncytial knots in the context of basal plate myofibers (if present but not mentioned) indicates higher recurrence risk for placenta accreta spectrum in future pregnancies 2
• Maternal vascular malperfusion findings warrant closer surveillance in subsequent pregnancies for recurrence of hypertensive disorders or growth restriction 2