Identifying an optimal inter-twin weight discordance cutoff for predicting donor survival after fetoscopic laser surgery for twin-twin transfusion syndrome.

BACKGROUND

Increased inter-twin growth discordance has been associated with adverse pregnancy outcomes. An inter-twin growth discordance of at least 25% is often considered as a clinical threshold for pathological discordance in unselected monochorionic-diamniotic (MCDA) twins, but an optimal cutoff for predicting survival outcomes following fetoscopic laser surgery (FLS) for twin-twin transfusion syndrome (TTTS) is unclear.

OBJECTIVES

This study aimed to (1) compare outcomes of FLS for TTTS based upon on the presence or absence of discordance ≥25%, (2) evaluate the association of different inter-twin discordance thresholds on donor twin survival after FLS, and (3) identify an optimal discordance cutoff for the prediction of donor twin survival.

STUDY

DESIGN

Retrospective review of MCDA twins with TTTS that underwent FLS at a single center from 2009 to 2022. The primary outcome was donor twin survival at first sonogram after FLS. Pregnancies with preoperative inter-twin discordance ≥25% were compared to those <25%. Differing thresholds of inter-twin discordance were compared to determine predictive accuracy for donor twin survival, and discordance was examined as a continuous variable to determine an optimal cutoff for donor twin survival prediction.

RESULTS

A total of 169 MCDA pregnancies underwent FLS and met inclusion criteria and 62 (37%) had inter-twin discordance ≥25%. Patients with inter-twin discordance ≥25% were younger (32±5 years vs 30±6 years, p=.03). Gestational age at TTTS diagnosis and at FLS were similar between groups. Donor twin selective fetal growth restriction (sFGR) was more likely with discordance ≥25% (74.2% vs 23.4%, p<.01). Pre-FLS Quintero stage differed between the 2 groups (p=.014), with higher likelihood of stage III and IV disease in the ≥25% group. Discordance ≥25% was associated with lower donor twin survival at first post-FLS sonogram (75.8% vs 89.7%, p=.02) and at newborn hospital discharge (52.8% vs 73.6%, p=.04). After adjusting for age, Quintero stage, and donor FGR, donor twin survival at first sonogram remained lower in patients with discordance ≥25% (p=.01). Discordance cutoffs of ≥25% and ≥30% were significantly associated with decreased donor twin survival at first sonogram post-FLS (p=.03 and p<.001, respectively) and this was true after adjusting for donor fetal growth restriction and pre-FLS Quintero stage. In fitting a logistic regression model, discordance as a continuous variable was significantly associated with predicting donor twin survival (p=.02). The area under the curve (AUC) for predicting donor twin survival was 0.63 (95% CI: 0.49, 0.74, p=.06). Based on the Youden index, the optimum cut point was a discordance of 29%, which had a sensitivity of 0.75, specificity of 0.58, positive predictive value of 0.91, and negative predictive value of 0.29 for predicting donor twin survival.

CONCLUSION

Discordance ≥25% was associated with lower donor twin survival after FLS for TTTS; however, inter-twin discordance alone is a poor predictor of donor twin survival after FLS for TTTS. If it is to be considered for use in clinical practice, a cutoff value of 29% was most predictive of donor twin survival in this cohort and may be useful for preoperative counseling on expected outcomes.