Pulmonary (Valvular) Stenosis and Its Link to Laser Therapy in TTTS

Why pulmonary stenosis develops in TTTS

• Cardiomegaly, biventricular hypertrophy, and diastolic dysfunction
• Increased right ventricular afterload and outflow tract hypertrophy
• Right ventricular outflow tract obstruction (RVOTO) — a spectrum ranging from functional/dynamic pulmonary stenosis (due to infundibular muscle hypertrophy narrowing the outflow tract) to fixed/structural pulmonary valve stenosis or even pulmonary atresia if the process goes unchecked

Association with laser therapy

• Functional/early RVOTO: Because the obstruction is driven by volume/pressure overload rather than a fixed anatomic valve lesion, successful fetoscopic laser ablation of the placental anastomoses removes the hemodynamic insult. As right ventricular performance normalizes, flow across the pulmonary valve can improve — laser therapy has been shown to improve or resolve early functional pulmonary outflow obstruction in a meaningful proportion of cases (Moon-Grady et al., Ultrasound Obstet Gynecol 2011, cited via MDPI review above).
• Fixed/structural RVOTO: Once the valve leaflets or infundibulum have undergone true structural remodeling (thickened, dysplastic, or atretic valve), laser therapy corrects the underlying TTTS physiology but does not reverse the anatomic valve damage. Recent postnatal follow-up data show that of recipient twins with RVOT anomalies treated by laser, about 27% resolve after laser, while the remainder persist after birth, and roughly 27% of those require a postnatal cardiac valve procedure (e.g., balloon pulmonary valvuloplasty) - PMC11266639.
• Established pulmonary stenosis at diagnosis carries a notably higher risk of remaining a major structural congenital-heart-disease finding compared with pulmonary insufficiency alone (hazard ratio ~4.7 in one cohort), meaning pulmonary stenosis specifically is less likely than pulmonary regurgitation to resolve with laser.
• Case reports confirm real-world persistence: a recipient twin with TTTS and pulmonary valve stenosis required successful postnatal balloon valvuloplasty, despite TTTS having been addressed (Golbabaei et al., BMC Pediatr 2023, PMID: 37400786); similarly, earlier reports (Murakoshi 2000) describe recipients needing neonatal balloon valvuloplasty after prenatal diagnosis of pulmonary stenosis in TTTS.

Practical implications

1. Timing matters - the earlier TTTS is treated with laser (before structural valve remodeling sets in), the better the chance that RVOTO is reversible.
2. Post-laser surveillance is required - recipient twins need serial fetal echocardiography after successful laser to track whether pulmonary flow/RVOT anatomy normalizes or persists.
3. Postnatal cardiology follow-up is mandatory for any recipient twin with prenatally diagnosed pulmonary stenosis, since a substantial subset will need neonatal intervention (balloon valvuloplasty being first-line) regardless of successful placental laser ablation.
4. Laser therapy treats the TTTS process, not necessarily the established cardiac lesion - the two should be thought of as related but distinct treatment targets.

Note on recent evidence