Supplementary Material for: The impact of maternal body mass index on fetoscopic laser surgery for TTTS

Background
Both a low and an increased body mass index (BMI) are risk factors for surgical complications. It is less clear whether they also affect the outcomes of fetoscopic procedures. In this manuscript we aimed to assess the effect of maternal BMI on operative and pregnancy outcomes following fetoscopic laser ablation of placental anastomoses for twin-twin transfusion syndrome (TTTS).
Methods
We retrospectively reviewed all patients with twin pregnancies complicated by TTTS treated with fetoscopic laser surgery at the Ontario Fetal Centre, Toronto over a 24 year period. Demographic and procedural data as well as pregnancy and delivery outcomes were prospectively collected as part of our quality control program. Patients were divided into 6 groups for BMI at the time of surgery: BMI <20, 20-24.9, 25-29.9, 30-34.9, 35-39.9 and ≥40kg/m2. Collected variables included demographics, operative characteristics, operative complications, obstetric complications, TAPS, TTTS recurrence, intrauterine (fetal) death (IUFD), gestational age (GA) at delivery and survival. Outcomes of all groups were compared to the ‘normal weight’ reference cohort (BMI 20-24.9kg/m2).
Results
Of 1,012 patients in our database, 859 were twin pregnancies treated with laser for TTTS. Pregnancy outcomes were available for 515. Of all patients, 40% were categorized as normal weight, 8% were underweight, 24% were obese and 4% had a BMI > 40kg/m2. Patients with a higher BMI had higher parity (p=0.0001), longer cervical length (p=0.008) and a significantly higher TTTS stage (p=0.0003) at the time of surgery. There were no significant differences between groups in terms of surgical or anaesthetic characteristics or perinatal complications. Patients with a higher BMI however, had a lower number of anastomoses ablated at the time of surgery (p=0.047).
Conclusion
BMI does not significantly affect operative or perinatal outcomes in patients undergoing fetoscopic laser ablation for severe TTTS, despite being at a higher stage at diagnosis.

背景
体质量指数（BMI）过低与过高均为手术并发症的危险因素，但目前尚不明确其是否同样会对胎儿镜手术的结局产生影响。本研究旨在评估母体体质量指数对双胎输血综合征（TTTS）患者行胎儿镜下胎盘吻合血管激光凝固术后的手术及妊娠结局的影响。

方法
本研究回顾性分析了24年间于多伦多安大略胎儿医学中心接受胎儿镜激光手术治疗的双胎妊娠合并双胎输血综合征患者的临床资料。作为本中心质控项目的一部分，人口统计学资料、手术相关数据以及妊娠与分娩结局均采用前瞻性收集方式。根据手术时的体质量指数，将患者分为6组：BMI<20、20~24.9、25~29.9、30~34.9、35~39.9以及≥40kg/m²。收集的变量包括人口统计学特征、手术相关特征、手术并发症、产科并发症、双胎贫血-多血质序列征（TAPS）、双胎输血综合征复发、宫内（胎儿）死亡（IUFD）、分娩时孕周（GA）以及胎儿存活率。以体质量正常的参照队列（BMI 20~24.9kg/m²）为对照，比较各组间的结局差异。

结果
本研究数据库中共纳入1012例患者，其中859例为接受激光手术治疗的双胎输血综合征双胎妊娠患者，515例具备完整妊娠结局资料。所有患者中，40%体质量正常、8%为体质量过低、24%为肥胖，4%的BMI≥40kg/m²。体质量指数更高的患者，手术时的产次更高（p=0.0001）、宫颈长度更长（p=0.008），且双胎输血综合征分期显著更高（p=0.0003）。各组间手术或麻醉相关特征以及围产期并发症均无显著差异。但体质量指数更高的患者，手术中需凝固的吻合血管数量更少（p=0.047）。

结论
尽管诊断时双胎输血综合征分期更高，但体质量指数并不会对重度双胎输血综合征患者行胎儿镜激光凝固术的手术结局或围产期结局产生显著影响。