Selective fetal growth restriction type II: IIb or not IIb

Monochorionic diamniotic twins have distinct risk profiles because of their single shared placenta. Selective fetal growth restriction complicates monochorionic diamniotic twin pregnancies by up to 25% because of unequal placental share, vascular anastomoses (aberrant sizes, quantities, and types), and discrepant cord insertion sites. Since 2007, the Gratacos classification system has been used to better understand the risk of selective fetal growth restriction based on the umbilical artery Doppler findings of the selective fetal growth restriction fetus, where type I has forward diastolic flow, type II has persistent absent or reversed end-diastolic flow, and type III has intermittent absent or reversed end-diastolic flow. Type I has an excellent prognosis, and type III is characterized by its unpredictable clinical course. This review focuses on early selective fetal growth restriction type II, which is generally considered to predict the worst outcome, with high rates of perinatal morbidity and mortality. Despite selective fetal growth restriction being relatively common, the optimal management remains controversial. Management strategies include expectant management, cord occlusion of the smaller twin to protect the appropriate grown twin, and selective laser photocoagulation of communicating vessels to unlink the fates of the twins. The clinical course of selective fetal growth restriction type II is not uniform, and a nuanced approach plays a role. Our study describes the management dilemma associated with early selective fetal growth restriction type II overall and the justification for the subclassification into type IIa vs type IIb, which may help stratify patients' prognoses and management plans.