What are the risks associated with a single bilobed placenta in a twin pregnancy?

Risks of a Bilobed (Bipartite) Placenta in Monochorionic Twin Pregnancy

A bilobed placenta in monochorionic twins is associated with significantly increased complications, particularly twin-twin transfusion syndrome (TTTS) occurring in 60% of cases, selective intrauterine growth restriction (sIUGR) in 20%, and creates substantial technical difficulties for fetal interventions when needed. 1

Key Clinical Risks

High Rate of Twin-Specific Complications

• TTTS develops in 60% of monochorionic twins with bipartite placenta, which is substantially higher than the baseline 9% TTTS rate in standard monochorionic pregnancies 1, 2
• Selective intrauterine growth restriction occurs in 20% of these cases 1
• Severe fetal malformations are seen in 20% of affected pregnancies 1
• The overall fetal survival rate at birth is 90%, but neonatal survival drops to only 66.63% due to complications 1

Surgical and Intervention Challenges

• Fetal interventions are indicated in 100% of bipartite placenta cases, but technically feasible in only 60% due to poor surgical conditions created by the separated placental masses 1
• The spatial separation of placental lobes makes fetoscopic laser coagulation of vascular anastomoses extremely difficult when treating TTTS or other complications 1
• This technical limitation significantly impacts the ability to provide definitive treatment for life-threatening conditions 1

Diagnostic Pitfall: Mimics Dichorionic Placentation

• A critical diagnostic error can occur because two separate placental masses on ultrasound may falsely suggest dichorionic (lower-risk) pregnancy when the pregnancy is actually monochorionic (higher-risk) 3
• The presence of two distinct placental masses with separate cord insertions has lower specificity for determining chorionicity, particularly in the second trimester 3
• Always confirm monochorionicity by identifying the T-sign at 11-14 weeks gestation, which is the most specific ultrasound marker, rather than relying on placental mass appearance alone 4, 3

Underlying Pathophysiology

• Monochorionic twins inherently carry over 2-fold higher perinatal mortality compared to dichorionic twins (7.6% vs 1.6% fetal demise rate) due to shared placental circulation with vascular anastomoses 4
• Bipartite placenta represents an extreme form of unequal placental sharing, which disrupts the normal compensatory mechanisms of intertwin vascular connections 2
• The separated placental lobes create more elaborate blood exchange patterns that can paradoxically worsen hemodynamic imbalances between twins 2

Management Implications

• Intensive surveillance every 2 weeks starting at 16 weeks is mandatory for all monochorionic pregnancies, with even closer monitoring warranted when bipartite placenta is identified 4
• Early referral to a tertiary fetal therapy center is essential given the near-universal need for intervention and technical complexity 1
• Counseling should address the 33% neonatal mortality risk and high likelihood of requiring complex fetal procedures 1
• If intervention becomes impossible due to placental anatomy, umbilical cord coagulation for selective feticide may be the only option to protect the healthier co-twin, with 83% survival and 92% normal development rates 2