This multicenter tudy compared maternal and neonatal outcomes in parturients who attempted preterm TOLAC to term TOLAC. Despite the increased risk for in labor CD in the preterm group, overall maternal outcomes were comparable and favorable. Neonatal outcomes were generally less favorable among the preterm group, as expected. However, the 5-minute Apgar score was not independently associated with preterm TOLAC. VBAC rates in this study were significantly lower in preterm TOLAC, 57%; compared with 80% in the term TOLAC. Previous studies have described equivalent 19 or higher20 VBAC rates in preterm TOLAC (72–82%) compared to term TOLAC. Factors such as, diabetes mellitus and hypertensive disorders of pregnancy 21, 22, 23 previously linked to VBAC failures were significantly more prevalent among preterm TOLAC parturients in this study. Performing a multivariate logistic regression, both above-mentioned factors were found independently associated with in-labor CD. Similar to other studies, the current research found epidural analgesia to be a protective factor of in-labor CD.24 We propose that the contribution of these factors most likely have the same effect on TOLAC in the preterm population as in the term population and should be further studied. The relatively lower VBAC rate in our institution compared to other centers might be attributed to special characteristics of our study population. In both study centers the parturients are mostly characterized by high order of parity, and therefore TOLAC is advocated. Nonetheless, we employ a conservative approach in these high-risk deliveries, and are vigilant with our decision-making during the labor process, which may tend to result in a higher rate of in-labor cesarean.
Maternal outcomes in our study were generally favorable. The rate of uterine rupture, which is one of serious complication of TOLAC, was comparable between groups. Both Quiñones et al 20 and Durnwald et al19, compared maternal morbidity in preterm versus term TOLAC. They found lower rate of uterine rupture in preterm TOLAC than term deliveries. These studies postulated that the lower rates of uterine rupture at preterm TOLAC were a result of lower birthweight and thicker lower uterine segment in preterm gestations compared with those at term. Comparable to Durnwald's study19 our study established that maternal blood transfusion is prevalent in parturients attempting preterm TOLAC than those at term. We propose that the reasons for coagulopathy and blood transfusion in preterm TOLAC are related to higher rates of pathological causes for preterm delivery such as abruption and preeclampsia, rather than exclusively preterm TOLAC. Many preterm deliveries are linked to preterm premature rupture of membrane (PPROM) and chorioamnionitis. 10 Endometritis is a common result of both chorioamnionitis as well as PPROM. Surprisingly, the rates of endometritis in our study were significantly lower in preterm TOLAC compared to term, similar to those in Durnwald et al study19.
Likewise, neonatal outcomes in this study were less favorable in preterm TOLAC compared to term. This is not surprising, as preterm neonates are at high risk for mortality and adverse health outcomes. Durnwald et al19 compared preterm TOL to RCD reported similar neonatal outcomes such as Neonatal Intensive Care Unit (NICU) admission, intraventricular hemorrhage, sepsis, and ventilatory support, after controlling for gestational age at delivery in preterm TOLAC with the exception of a higher rate of respiratory distress syndrome in those delivered after a TOLAC. Other studies that investigated outcomes of preterm birth by mode of delivery did not determine that the mode of delivery affected neonatal outcome. 13, 14, 15 Furthermore, previous studies 25, 26, 27 determined that the bacterial inhabitants of the neonatal respiratory tract (i.e. Microbiome) differ between those who delivered vaginally compared to those who had CD. The vaginal flora has a favorable effect on neonatal respiratory illnesses in both short and long term.26 In addition, studies28, 29 that evaluated the respiratory performance of lambs following vaginal vs cesarean deliveries, demonstrated that lambs who delivered vaginally had better respiratory performance. This was attributed to the reduction of lung liquid volume achieved throughout delivery. This effect was not reached to the same extent in lambs whose lung volume was artificially reduced. It is well established in the literature30 that the neonatal respiratory morbidity when comparing cesarean to vaginal delivery, is not solely related to gestational age at delivery and that vaginal delivery itself has a favorable effect on the neonates' respiratory status. In our study, it was difficult to evaluate the impact of prematurity itself in the preterm group on the neonatal outcomes. A comparison of elective CD versus TOL should be performed in this specific population in order to characterize the specific contribution of TOL to neonatal outcomes in the preterm population.
This study has several strengths. The study addresses an important issue with limited data. Success and safety of preterm TOLAC have not been extensively studied before.
We performed a large-scale population multicenter study comprising more than a half of the births in the Jerusalem vicinity and about 16% of all national births. These two factors contribute to the generalizability of our findings. In addition, our database is validated in real-time, which assists in eliminating potential information bias. Over 95% of Israeli citizens’ medical care is covered by the Israeli National Health Plan, hence continuity of care is granted, and all costs of antenatal care, birth, postpartum care for mother and child are uniformly covered for the entire study period. Moreover, all mother-child data included were solely from the medical centers involved in this study with no transfers to other facilities. These factors alleviate a potential selection bias.
Conversely, our study has several limitations, primarily its retrospective nature. We recognize that our data collection process did not provide information regarding potential risk factors associated with successful VBAC such as the indication for previous CS. Nonetheless, we did attempt to control for most recognized factors and excluded all identified parturients who did not meet the ACOG criteria for TOLAC.31
In conclusion, in our study, preterm TOLAC has lower success rates, but similar maternal morbidities compared to TOLAC at term. Prospective studies are required to better evaluate the neonatal results in the preterm TOLAC population. Overall, preterm TOLAC seems to be a safe method of delivery. We suggest that this information be presented in the pre-delivery counseling process to this subset of parturients.