Risk factors for spontaneous preterm delivery in monochorionic diamniotic pregnancies undergoing selective fetal reduction via radiofrequency ablation.

Introduction: To identify risk factors for spontaneous preterm delivery (sPTD) before 32-, 34- and 37-weeks in a cohort of monochorionic diamniotic (MCDA) twin pregnancies undergoing selective fetal reduction (SFR) using radiofrequency ablation (RFA).

Methods: A single center retrospective analysis of complex MCDA twin pregnancies managed with SFR via RFA between 2014-2023. Perioperative variables were compared between patients who had sPTD before and after 34 weeks and 37 weeks. We also compared variables for pregnancies that delivered before and after 32 weeks. Correlation analysis between gestational age at SFR and gestational age at delivery was performed. Kaplan-Meier survival analysis was created for time to 34 weeks grouped by different diagnostic indications and log-rank test was performed.

Results: In the study cohort, the total rate of preterm delivery was 52.0% of these 46.9% pregnancies delivering spontaneously. The rate of sPTD before 34 weeks was 27.1% and before 32 weeks was 19.4%. There was a significantly higher proportion of pregnancies undergoing RFA for the indication of TTTS that delivered before 34 weeks (43.5% vs 22.6%, p=0.01). Also, a greater number of pregnancies undergoing RFA for the indication of TTTS delivered before 37 weeks spontaneously (35.7% vs 20.9%, p=0.04). A subgroup analysis of sPTD before 32 weeks was performed. Preoperative cervical length was the only independent predictor for delivery before 32 weeks on multiple regression after controlling for confounders. Gestational age at procedure did not correlate with gestational age at delivery (p=0.78). Kaplan-Meier curves showed that the proportion of pregnancies remaining undelivered from the time of RFA until 34 weeks' gestation was lower for the indication of TTTS.

Conclusion: Preoperative indication of TTTS was associated with an increased risk of sPTD before 34 and 37 weeks in the MCDA twin population undergoing RFA. In contrast, preoperative cervical length was independently associated with sPTD before 32 weeks in the same population.