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

Abstract

Subclassification of monochorionic twins with selective fetal growth restriction (sFGR) type II into IIa vs. IIb has been proposed due to differing neonatal survival outcomes of the growth-restricted fetus after laser surgery based on preoperative Doppler findings in the middle cerebral artery (MCA) and ductus venosus (DV). There is substantial clinical overlap between sFGR and twin-twin transfusion syndrome (TTTS). To compare donor twin neonatal survival after laser surgery in cases of TTTS with concomitant donor FGR type IIa vs. IIb. This is a retrospective study of monochorionic multifetal gestations treated with laser for Stage III TTTS and concomitant donor twin FGR type II at a referral center from 2006-2021. Donor FGR type II was defined as having an estimated fetal weight (EFW) <10th percentile with persistent absent and/or reversed end diastolic velocity in the umbilical artery. Patients were then subclassified as type IIa (having normal MCA peak systolic velocities [psv] and DV Doppler waveforms) vs. type IIb (having MCA psv ≥1.5 multiples of the median and/or DV with persistent absent or reversed atrial systolic flow). We compared 30-day neonatal survival of the donor twin by FGR type IIa vs. IIb using logistic regression to adjust for relevant preoperative covariates (p<0.10 in bivariate analysis). Of 919 patients who underwent laser surgery for TTTS, 262 had Stage III donor or donor/recipient TTTS; of these, 189 (20.6%) had concomitant donor FGR type II. Twelve met exclusion criteria, yielding 177 patients (19.3%) who comprised the study cohort. Patients were subclassified as donor FGR type IIa (146 [82%]) vs. type IIb (31 [18%]). Donor neonatal survival for FGR type IIa vs. IIb was 71.2% vs. 41.9% (p=0.003). Recipient neonatal survival did not differ between the two types (p=1.000). Patients classified with TTTS and concomitant donor FGR type IIb were 66% less likely to have neonatal survival of the donor after laser surgery (adjusted OR=0.34, 95% CI 0.15-0.80; p=0.0127). The logistic regression model was adjusted for gestational age at the procedure, EFW percent discordance, and nulliparity. The c-statistic was 0.702. For patients with Stage III TTTS and concurrent donor FGR with persistent absent or reversed end diastolic velocity in the umbilical artery (i.e., FGR type II), subclassification into FGR type IIb based on elevated MCA psv and/or abnormal DV flow in the donor conveyed poorer prognosis. Although donor neonatal survival after laser surgery was lower for Stage III TTTS patients with donor FGR type IIb compared with type IIa, laser surgery for FGR type IIb in the setting of TTTS (as opposed to pure sFGR type IIb) still allows for the possibility of dual survivorship and should be offered with shared decision-making when counseling patients on management options.