Selective Fetal Growth Restriction in Monochorionic Twin Pregnancy: A Practical Framework for Intervention

Selective fetal growth restriction (sFGR) complicates 10–15% of monochorionic (MC) twin pregnancies. Because the twins share one placenta connected by vascular anastomoses, the smaller twin depends on its co-twin, and the death of one twin puts the survivor at risk of death and brain injury. sFGR is therefore not simply fetal growth restriction with an extra fetus. This review provides a practical framework for clinicians. Diagnosis should rely on the Delphi consensus criteria and twin-appropriate growth standards. The Gratacós classification, based on umbilical artery Doppler of the smaller twin, separates three clinical behaviors: type I is usually low risk, type II is usually severe and type III is unpredictable. Onset before or after 24 weeks adds information about placental anatomy and the likelihood of twin anemia-polycythemia sequence. The three management options are expectant management, fetoscopic laser coagulation of the anastomoses and selective reduction. None is free of risk. Expectant management is preferred for type I. In types II and III, laser increases the loss of the smaller twin but may protect the larger twin, while selective reduction prolongs pregnancy and improves intact survival of the larger twin in selected cases. We suggest considering intervention when demise of the smaller twin appears imminent, particularly before viability. When sFGR coexists with twin-twin transfusion syndrome, laser treats the transfusion imbalance but not the unequal placental share. Counseling should begin by agreeing with parents on the outcome they most wish to protect.