Subclassification of fetal growth restriction type IIa vs type IIb applied to twin-twin transfusion syndrome

BACKGROUND: Subclassification of monochorionic twins with selective fetal growth restriction type II into IIa vs IIb has been proposed because of differing neonatal survival outcomes of the fetus with growth restriction after laser surgery based on preoperative Doppler findings in the middle cerebral artery and ductus venosus. There is substantial clinical overlap between selective fetal growth restriction and twin-twin transfusion syndrome. OBJECTIVE: This study aimed to compare donor twin neonatal survival after laser surgery in cases of twin-twin transfusion syndrome with concomitant donor fetal growth restriction type IIa vs IIb. STUDY DESIGN: This was a retrospective study of monochorionic multifetal pregnancies treated with laser surgery for stage III twin-twin transfusion syndrome and concomitant donor twin fetal growth restriction type II at a referral center from 2006 to 2021. Donor fetal growth restriction type II was defined as having an estimated fetal weight <10th percentile with persistent absent and/or reversed end-diastolic velocity in the umbilical artery. Moreover, patients were subclassified as type IIa (having normal middle cerebral artery peak systolic velocities and ductus venosus Doppler waveforms) vs type IIb (having middle cerebral artery peak systolic velocities ≥1.5 multiples of the median and/or ductus venosus with persistent absent or reversed atrial systolic flow). This study compared 30-day neonatal survival of the donor twin by fetal growth restriction type IIa vs IIb using logistic regression to adjust for relevant preoperative covariates (P<.10 in bivariate analysis). RESULTS: Of 919 patients who underwent laser surgery for twin-twin transfusion syndrome, 262 had sstage III donor or donor and recipient twin-twin transfusion syndrome; of these patients, 189 (20.6%) had concomitant donor fetal growth restriction type II. Moreover, 12 patients met the exclusion criteria, yielding 177 patients (19.3%) who composed the study cohort. Patients were subclassified as donor fetal growth restriction type IIa (146 [82%]) vs type IIb (31 [18%]). Donor neonatal survival for fetal growth restriction type IIa vs IIb was 71.2% vs 41.9% (P=.003). Recipient neonatal survival did not differ between the 2 types (P=1.000). Patients classified with twin-twin transfusion syndrome and concomitant donor fetal growth restriction type IIb were 66% less likely to have neonatal survival of the donor after laser surgery (adjusted odds ratio, 0.34; 95% confidence interval, 0.15–0.80; P=.0127). The logistic regression model was adjusted for gestational age at the procedure, estimated fetal weight percent discordance, and nulliparity. The c-statistic was 0.702. CONCLUSION: For patients with stage III twin-twin transfusion syndrome and concurrent donor fetal growth restriction with persistent absent or reversed end-diastolic velocity in the umbilical artery (ie, fetal growth restriction type II), subclassification into fetal growth restriction type IIb based on elevated middle cerebral artery peak systolic velocity and/or abnormal ductus venosus flow in the donor conveyed poorer prognosis. Although donor neonatal survival after laser surgery was lower for patients with stage III twin-twin transfusion syndrome with donor fetal growth restriction type IIb than patients with stage III twin-twin transfusion syndrome with donor fetal growth restriction with type IIa, laser surgery for fetal growth restriction type IIb in the setting of twin-twin transfusion syndrome (as opposed to pure selective fetal growth restriction type IIb) still allows for the possibility of dual survivorship and should be offered with shared decision-making when counseling patients on management options.