Operative characteristics and pregnancy outcome
The operative characteristics and pregnancy outcomes were showed in table 2. There was no significant difference between the two groups in the operative characteristics. The cervical length before procedure and the total ablation time were non-significant. The rate of preterm birth before 37 weeks, before 34 weeks, before 32 weeks ,before 30 weeks and before 28weeks were similar between the two groups. The complication after the procedure in the two group were non-significant different, including post-procedural complication and perinatal complication. Termination of pregnancy(TOP) due to fetal serious oligohydramnios or structural anomaly of the co-twin. TOP occurred in 8 cases in fetal abdomen group and 3 cases in fetal back group. The TOP rate was non-significant different in the two group(6.9% vs 10.3,p =0.53). The characteristics about delivery were non-significant different between the two groups too, including the neonatal gestational age and the rate of cesarean section.
The relation of RFA technique was assessed by means of survival analysis. Multivariate Cox regression analysis indicated that the survival curve of fetal survival time interval after the procedure between the two needle insert angles were statistically different, while set several related variables as covariates, including gestational age at the procedure, cervical length, indications and total ablation time. (P <0.001)(Figure 2). The model characteristic was showed in table 3, cervical length and the gestational age before the procedure were significant predictors for the period between RFA procedure and delivery(table 3).
Risk of adverse outcome of the RFA procedure: multivariable analysisMultivariable logistic analysis was conduct to assess the relation of the risk of perinatal adverse outcome and several factors, include different RFA needle insert angle, gestational age at the RFA procedure cervical length before the procedure, the overall ablation time, while controlling for maternal age and indication for RFA as potential confounders. The result showed that compared to live birth at term, the risk of miscarriage,termination and IUFD were statistically higher when the cervical length was less than 35mm( Table 4). The model revealed that the subject cervical length less than 27mm were 33.416 times to report adverse perinatal outcome than those whose cervical length more than 35mm. While other factors were non-significantly related with a higher rate of adverse perinatal outcome, including miscarriage, IUFD, termination and preterm birth.Factors associated with risk of advertise outcomeWe further assessed the association between the indication for RFA and the risk of adverse post-procedure complication. Overall, 49(33.8%) RFA were conducted due to TTTS, 30(20.7%) due to anomalous co-twin, 23(15.9%) due to sIUGR, 19(13.1%) due to TRAP, 12(8.3%) due to excessive number of fetuses, 11(7.6%) due to TTTS accompanied by sIUGR, 1(0.7%) due to TAPS. Table 5 showed the outcome variables stratified by indication. Table 5 showed the outcome variables stratified by indication.The gestational age at the procedure was significantly different within the indications, those who underwent RFA for TRAP and excessive number of fetuses were lower than monochorionic twin pregnancy complications. Women who underwent RFA for TTTS had a similar gestational age at the procedure as who underwent RFA for TTTS, TTTS & sIUGR. The interval between RFA procedure and delivery was statistically different within the indications, the interval of those who underwent RFA for excessive numbers of fetuses was longer than other indications. The preterm labor(<37weeks) rate was statistical different within the indications, those who underwent RFA for TTTS was later than any other indications. Even though there was non-significantly different during the indications, the gestational age at delivery of TTTS was lower than other indications.Even though there was non-significant difference within the indications, the pregnancy with live born fetus showed a higher trend in IUGR &TTTS and excessive number of fetuses than other indications. In order to assess the impact of gestational age at the RFA procedure on perinatal outcome, we conduct a subgroup analysis, according to whether the procedure was performed before 24weeks or after 24 weeks, the age of viability2.(table 6) Overall, 117 RFA procedures were performed before 24 weeks gestational age, and 28 RFA procedures were performed after 24 weeks gestational age. In order to avoid serve preterm birth, the RFA procedure were conducted before 28 weeks. There was no significant difference between the subgroups with regard to total ablation time, alive rate, adverse perinatal outcome rate, gestational age at delivery and preterm labor. The interval between RFA procedure and delivery was statistically shorter in post-viability group than in pre-viability group.