Selective FGR in Monochorionic Twins: Gratacós Classification I–III and Surveillance Strategy
Definition and Classification Basis
Selective fetal growth restriction (sFGR) in monochorionic pregnancy is classified according to the Gratacós system (Ultrasound Obstet Gynecol, 2007) based on the pattern of blood flow in the umbilical artery of the smaller twin.
Types I–III According to Gratacós (ISUOG, 2025)
| Type | Doppler Spectrum in Umbilical Artery of Smaller Twin |
|---|---|
| Type I | Positive end-diastolic flow |
| Type II | Absent or reversed end-diastolic flow (AREDF) |
| Type III | Cyclical/intermittent pattern of AREDF (intermittent absent or reversed end-diastolic flow) |
Surveillance and Management Strategy
According to ISUOG Practice Guidelines (2025), the evidence base for managing monochorionic twins with sFGR is limited. When there is substantial risk of intrauterine fetal demise of one twin before 26 weeks, selective reduction may be considered (GRADE OF RECOMMENDATION: D).
For type III (intermittent AREDF), fetoscopic laser coagulation of placental anastomoses has been described in the literature as an active management approach (Gratacós et al., Ultrasound Obstet Gynecol, 2008). Specific intervals for dynamic surveillance and threshold gestational ages for delivery by type are not provided in the source fragments — [to be clarified].
Frequently asked questions
By what parameter are types I–III sFGR differentiated?
By the pattern of Doppler spectrum in the umbilical artery of the smaller twin: type I — positive end-diastolic flow, type II — persistent AREDF, type III — cyclical/intermittent AREDF (Gratacós, 2007; ISUOG, 2025).
When is selective reduction considered?
Selective reduction may be considered when there is substantial risk of intrauterine fetal demise of one twin before 26 weeks (GRADE OF RECOMMENDATION: D, ISUOG, 2025).
What method is described for type III?
Fetoscopic laser coagulation of placental anastomoses for intermittent AREDF (type III) with assessment of perinatal outcome (Gratacós et al., Ultrasound Obstet Gynecol, 2008).
How robust is the evidence base for managing sFGR?
According to ISUOG (2025), the evidence for the management of monochorionic twins with sFGR is limited.